Korosensei

Overview

Image Gallery

Korosensei
Kanji	殺せんせー
Romaji	Koro-sensei
Alias	Octopus The Grim Reaper (formerly) The Tentacled Menace (by Karasuma) Guinea Pig (by Shiro) Demon King (in Koro-Sensei Q!) Prince of the Fateful Eternal Wind (Self-given codename) Octopus of the Idiotic Perverted Chicken (Codename given by students) Octorazzi (by Irina)
Character Information
Birthday	March 12 (given; Pisces)
Gender	Alien Male
Height	3m (9'8ft)
Weight	lighter than he looks
Blood Type	AB
Status
School	Kunugigaoka junior high school
Class	3-E
Seat Number	None
Affiliation	Kunugigaoka Junior High School
Occupation	Homeroom Teacher of Class 3-E Assassination Target Assassin (Formerly) Demon King (Koro Q) Hero (Former)(Koro Q)
Status	Deceased (manga/anime) Alive (movie/in Koro-Sensei Q)
Debut
Manga	Chapter 1
Anime	Episode 1
Portrayal
Japanese Voice	Jun Fukuyama (Anime and 3Ds Game) Tomokazu Seki (OVA and J-Stars Victory VS) Masaya Onosaka (VOMIC)
English Voice	Sonny Strait (Funimation)
Actor	Kazunari Ninomiya

“	The tentacles asked him "what do you want to be?" and he answered "I want to be weak." A creature that appears helpless, something so ridiculous that you want to just squeeze him to death! Something that can suss out the vulnerabilities in other creatures with its tentacles, that can protect them, and lead them. That was the creature... no... the teacher... he wanted to become.	”
— Korosensei's goal

Koro-sensei (殺ころせんせー, Koro-sensei) is a main character in the Assassination Classroom series.

He was the homeroom teacher of Class 3-E at Kunugigaoka Junior High School, and was heavily involved in the events of the series - including the deformation of Earth's moon into a permanent crescent. Prior to becoming a teacher, Koro-sensei was a contract killer, known as "The Reaper".

Appearance

Korosensei has the appearance of a yellow octopus who is about three meters tall and possessed a large, bulbous head with a large smile that rarely breaks or moves, and small, beady eyes. He uses two tentacles as arms, each having two feelers as fingers, and utilized the rest of seemingly jelly-like limbs - his tentacles - to walk. Korosensei has a pair of hidden nostrils, which make him appear to have four eyes if detected. Due to his constant grinning, he changes his color to express his emotions.

Korosensei wears a black academic dress, a small black squarish mortarboard cap with a yellow tassel and a large black tie with a yellow crescent-shaped moon on it, a gift from Aguri Yukimura.

As a human, he had pale skin, a slender build, dark eyes, and short black hair that reached to his nape. He sports an amicable smile, which was initially used to manipulate others. When carrying out assassinations, he donned formal clothing. After being taken prisoner by Kotaro Yanagisawa, he was put in patients' scrubs until his escape and transformation.

Personality

It was revealed that he was raised in an environment "where everybody could easily betray one another to the point that one could only trust oneself". Through these hardships, he decided to become an assassin to survive. Despite gaining an apprentice, he only saw him as a tool for his goals, which drove the latter to finally betray his master.

However, after meeting Aguri Yukimura, he finally knew what compassion really was--becoming much kinder as a result. According to Aguri, if he was born in a peaceful country, he would be "a little lecherous, smart, klutzy, kind of stingy and stubborn" and he would smile because he is genuinely a kind person. This prediction happens to reflect his personality; which became forefront after he answered the tentacles.

When first introduced, Korosensei was an upbeat individual who demanded absurd and seemingly mundane requests despite claiming he would be the cause of the planet's destruction in a year. He was also rather kind to others in general and could switch from silly and childish to serious on the fly. According to Nagisa Shiota, Korosensei also was unintentionally petty at others at times and loved gossip, both traits heavily noted throughout the series.

From time to time pieces of his old personality as The Reaper were visible such as when Ryoma Terasaka tried to sacrifice Nagisa to kill Korosensei and Korosensei menacingly threatened all of their families if they tried another self-harming attempt like that. In that moment, he resorted to his old method of teaching through fear. As the series progresses, his character development renders him more and more capable of true empathy and learning to use that empathy to teach lessons instead of through fear and reward like he had with his first student.

Korosensei deeply cared for his students' emotional and physical well-being and would lose his temper whenever any of them were put in danger, even by one another. On the annual school trip to Kyoto, a few of his students were assaulted/kidnapped by a gang of high schoolers hidden in an alley. After searching the entire area painstakingly, he infiltrated the abandoned building where two of his students, Yukiko Kanzaki and Kaede Kayano, were being held at and single-handedly beat up all of the high schoolers, scaring them away.

One of Korosensei's attributes was that he was able to connect to each student individually, being an objective, empathetic, and observant person who will do almost anything to help his students. This was why all the students respected him even though he would blow up the Earth in a year. Taking care of each student's needs, Korosensei would sometimes be piqued by a student's current problems or interests and would try his best to guide the student along or solve it for them.

Korosensei loved sweets almost to extreme cases, and was also shown to be a very perverted character, a trait he shares with his student Taiga Okajima and Itona Horibe. This characteristic was revealed to be the side effect of the experimentation with anti-matter tentacles which made him unable to hide his true feelings.

Etymology

Koro-sensei's name is a play on words. It is a portmanteau of the phrases 殺せない (korosenai, 殺せない), which means "unkillable", and 先生 (sensei, 先生), which means "teacher". It was given to him by Kaede Kayano.

History

As a child, he was born into one of the vilest and corrupt slums in an unknown country. He never knew his real name or his birthday. It was an environment where everybody could easily betray one another to the point that one could only trust oneself. Through these hardships, he learned that there are only three things you can really count on: skill, money and death. This ideology is what made him decide to become an assassin, eventually becoming the master assassin known as The Reaper after his one-thousandth kill. Those who were stronger than him, he killed with his intellect; those who were smarter, he killed with strength; those who were strong and smart, he killed with his charm. Immediately, his talents were shown as he left a tremendous trail of corpses in his wake. He became notorious for breaking through even the most strict security teams to assassinate his targets without any hitch.

All this changed after assassinating a wealthy businessman and father. The man's child witnessed the killing and became enamored with the beauty of the kill, requesting that the Reaper train him as his apprentice. Eager for the assassination opportunities that an apprentice could give, the Reaper took in the boy and trained him. He taught him everything he knew, all while still instilling respect and fear in him and letting him know the difference in power between them, although he only saw him as his tool rather than a real student.

The Reaper's apprentice betrays him.

After several successful jobs, the apprentice turned on The Reaper as he was attempting to escape a prison facility. The apprentice, later the current Reaper, sought his master's title and abandoned him just to fuel his ego. Betrayed, the Reaper was captured and thrown into an undocumented research laboratory run by Kotaro Yanagisawa. Yanagisawa's research goal was to create large amounts of organic antimatter by having it "piggyback" on the growth of human cells.

It was there that he met and befriended Aguri Yukimura, a teacher who was in an arranged and abusive marriage to Yanagisawa at the time. She was brought in to keep a closer eye on him as Yanagisawa considered her easily expendable if he attempted to break free and take her hostage. As the tests continued, the Reaper began to slowly bond with her and became fond of her as she worked on compiling exam questions for her class, and it was during this time he learned what compassion was.

One year after he had been imprisoned in the lab, Aguri got him a large tie as a present, since he would complain about his neck being cold and because he didn't know his actual birthday, she thought their anniversary was as good a day as any.

The Reaper in captivity.

However, a problem arose when Yanagisawa and his researchers questioned what would happen to Korosensei's antimatter cells when he died. To answer this question, Yanagisawa and his team launched a small automated lab onto the moon to safely test the possibility of what happened if a subject with Korosensei's antimatter-infused cells were to die, in this case, a small lab rat. When the rat did die at the end of its lifespan, it caused a volatile reaction with the antimatter in its body. The antimatter created a chain reaction that turned 70% of the moon's matter into antimatter, which completely exploded. Upon seeing this, Yanagisawa was horrified at the results. His subordinates then began running calculations and discovered that the same thing would happen to the Reaper by March 13 of the following year. Earth would be destroyed the same way if left unchecked, prompting Yanagisawa to order his subordinates to start preparations to kill him.

The transformed Reaper begins his escape.

A mortified Aguri overheard this and decided to go speak to the Reaper and tell him their findings. However, when she did, he revealed that it does not bother him as he expected a death such as this from the start. Telling Aguri to leave, he finally unleashes his full power that he gained from the experiments to escape as a visibly fuming Yanagisawa watches from a nearby security camera. The Reaper then proceeded to rampage violently, killing off several guards, destroying the building, and in the process of it all damaging Yanagisawa's left eye.

However, during the escape, Aguri is mortally wounded when she landed in the line of fire of a special trip-mine meant for him, to the latter's horror. He then laments that if he hadn't wasted his skills on killing, he would know how to save her. Her final wish to him was to teach the students of Class 3-E, all while thinking of what a wonderful teacher he would be. Depressed but not broken, the Reaper vowed to help those children. He took the tie Aguri got him, left a note, left the facility for a nearby mountain and then used various items on the mountain to create a new set of clothes to suit his new role as a teacher.

Although not responsible for destroying seventy percent of the moon, he took the blame and told the world's leaders that he would destroy the Earth as well in March of the following year and requests to become the homeroom teacher for Kunugigaoka Junior High School's Class 3-E. The world leaders accepted the deal, hoping it would give them a chance to assassinate him; however, they also added another condition: he would not harm the students.

Plot

Introduction: Assassination Time

Korosensei demonstrates his weakness to anti-sensei material.

As Korosensei starts the attendance, he asks Nagisa Shiota, who is on day duty, to issue command. Korosensei was ambushed by his students with automatic rifles, but he dodges the bullets while doing the attendance. Korosensei is pleased that there are no absentees, but he was also ashamed that nobody could hit him. He tells them that they should devise a plan together. The students complain that even if he were to get hit by the BB pellet bullets, he would just endure it. Korosensei demonstrates that those BB bullets, created specially in America for harming him, are harmless to the students and shoots his right feeler off. However, Korosensei regenerates his feeler back after a few seconds and warns them not to use them indoors except for killing him. He then tells them that they will kill him before graduation and decides to tidy the class up.

Later, he questions Masayoshi Kimura of which one of his four tentacles is the weird one, which Kimura responds that the blue tentacle is the odd one and Korosensei is then pleased with his correct answer. He then catches a bullet with his chalk. He becomes red and punishes Rio Nakamura, saying that her assassination meddles with her study. When lunchtime starts, Korosensei decides to go to China while grading his student's tests. Korosensei later casually came back with a missile souvenir after having been ambushed by the self-defense in the Sea of Japan. Nagisa asks him if it was troublesome that he was targeted, but Korosensei tells him that he doesn't mind, and that it shows proof of his vast power.

The class starts again and Korosensei decides to assign a poem and the one who is finished should bring it to him. Korosensei was asked by Kaede Kayano what name they should refer him as; Korosensei tells her that they can decide. Korosensei sees Nagisa walking up deliver the letter. He was suddenly struck by him, but he easily blocked it. However, Nagisa retaliates with a BB pellet grenade, much to Korosensei's surprise; but Korosensei uses his shed skin to protect himself and Nagisa, which he can only use once a month. After revealing his ability, he turns black with extreme anger and calls out the ringleaders of the BB pellet grenade. Korosensei then roams around town with his mach 20 speed and brought the nameplates from their houses. He tells the students: due to the agreement to not harm the students, if they try the same assassination method again, then he would annihilate anyone they know. He was questioned by Ryoma Terasaka of the degree of the assassination, and Korosensei corrects him by saying that it was excellent and praises Nagisa for keeping a natural body movement. However, Korosensei admonishes them of having no regard for Nagisa's life. He then advises them that they should use an assassination method that will make everyone happy and that they should use their hidden talents. After seeing a burn mark on a table, he remembers the incident from his past.

First Semester

Inspiring his class

Apart from avoiding every assassination attempt by the class, Korosensei teaches them valuable life lessons and give the individual students the confidence in themselves despite being placed in the discriminatory Class 3-E. When going up against the school's discriminatory education policy led by the board chairman Gakuho Asano, Korosensei lost in the mid term exams by having been focused too much on getting all of Class E ranked in the top 50. At the time however, it was also to teach the students the importance of "having a second blade" since in the event Korosensei is killed, the students still have to plan for their future in life regardless of who claims the ten billion yen bounty. During the exhibition match between Class E and the school's baseball club, Korosensei coached the class in countering the star player's pitches and helped them win despite Asano's interventions. While the students are grateful that their teacher is doing all of this for their benefit, they still get annoyed by his various antics, such as eavesdropping for juicy gossip and getting too cocky, which normally gets Korosensei into trouble.

During the semester, Korosensei had been challenged to a duel against the second transfer student Itona Horibe, accompanied by the mysterious Shiro. Much to his and everyone's surprise, Horibe has the same tentacle implants as Korosensei which explains why Horibe had earlier called Korosensei his 'brother'. Although visually disturbed by Itona's tentacles and the well planned strategies devised by Shiro, Korosensei outmaneuvers the pair and defeats Itona. Before Korosensei could get any answers regarding Itona's tentacles, the pair retreated but not before vowing to return. The pair kept their vow and returned to ambush Korosensei but he was rescued by the students who were none too pleased that they were used and almost killed indirectly by Shiro.

End of Term Time

With the finals approaching, Korosensei motivates the class into getting first place in any of the five subjects with the reward being that they have the right to shoot off one of his tentacles. Knowing that this will slow down his speed, the class takes up the challenge enthusiastically, but also got drawn into a wager with Class A. The results show that Rio Nakamura, Yuma Isogai and Manami Okuda scored first place in English, Social Studies and Science respectively. However, Korosensei has been conned to have four additional tentacles destroyed when Ryoma Terasaka, Kirara Hazama, Takuya Muramatsu and Taisei Yoshida tied for first place in Home Economics, a subject Korosensei tried unsuccessfully to disregard as not being a core subject. The class's plan is to attempt their ambitious assassination on a holiday island resort in Okinawa, which was the prize for winning their wager with Class A.

Assassination Island Arc

Arriving on the island resort, Korosensei participates in many activities with the class seemingly not knowing the true purpose of his students' agenda ahead of the assassination. At the end of the day, Korosensei has been sun burnt to the point that no one can read his burnt black face. He sheds his skin as his monthly routine, but unwittingly weakens himself and wasted one of his defense measures. The class then makes him watch an embarrassing film of his antics and unusual hobbies as a way to mentally weaken him. When it finishes, he realizes too late of the high tide as the seven shoot off his tentacles. From there, his surroundings change dramatically as the students trap him in a hydraulic water cage and fire anti-sensei BBs all around him. As he senses two BBs fired by Ryunosuke Chiba and Rinka Hayami, Korosensei was forced to use his last resort, turning himself into a ball with an unbreakable shield surrounding him at the cost of forsaking his mobility.

Later that night, 10 of his students collapse to an artificial virus. The mastermind behind the virus puts them to ransom and demands that Korosensei be delivered by Nagisa Shiota and Kaede Kayano to the mountain hotel in exchange for the antidote. Although unable to move, Korosensei assists the 15 remaining students to infiltrate the hotel and even helped call out commands while simultaneously distracting one of the hired hitmen. When the class discovers the mastermind as their short-lived PE teacher Akira Takaoka, Korosensei is forced to watch him and Nagisa battle it out for the antidote. The situation was so grave that Korosensei grew worried and even advised Tadaomi Karasuma to intervene should anything bad happens. Fortunately, Nagisa defeated Takaoka, and the ill students had never been in any danger; the virus was a fake. The next day, Korosensei was sealed away in concrete slabs by Karasuma in a vain effort to kill him, but he manages to return to his normal form.

Before leaving the island, Korosensei organized a Test of Courage. It is supposed to be a haunted attraction, but his ulterior motive is to create more juicy gossip by pairing up the students to spark any romances. The class immediately realizes what Korosensei had planned and the latter half of the pairs instead turned the tables on their teacher by making him scared.

Second Semester

Continuing to inspire

Much like the first semester, Korosensei continued teaching Class 3-E some valuable life lessons. He gave the class some practical experience to their newly-learned ability to free-run taught by Tadaomi Karasuma by organizing a game of Cops and Robbers and inspired Yuma Isogai to lead his class to victory against Class A during the Athletic Festival.

Korosensei briefly suffered a loss of trust with his students when they suspect him of crimes he did not commit due to his perverted hobbies. He was vindicated when he and a few skeptical students find the culprit to be Shiro and Itona Horibe, who once more ambush him using the same strategy employed by Class 3-E during the summer vacation. This time, Korosensei convinced Itona to join them after the latter was coldly abandoned by Shiro for the repeat failures and removed the tentacles from him.

Unwanted attention

Korosensei becomes livid after Class 3-E injures Matsukata.

As the mid-terms approached, some of the Class 3-E students started to take short cuts by studying and training at the same time, free-running through the town despite being expressly forbidden to do so. This soon gets them into trouble when they surprise an old man and cause him to break his leg. Korosensei was furious upon learning of this and slapped the students involved in his anger, despite the condition he was not to harm them. To teach them humility, Korosensei forbids them to study for two weeks and help out at the nursery the old man runs, which consequently lowered their test ranks, save for Karma Akabane.

The students' actions had also attracted the attention of the professional hit man known as the The Reaper. When Korosensei was away, the hit man took the class hostage to lure the target in and Korosensei was soon captured. They were later freed when Tadaomi Karasuma defeated the Reaper.

Nagisa's Time

Afterwards, Korosensei held a careers consultation for the class, wishing to know what their second blade will be should somebody succeed in killing him, while humorously avoiding each student's attempts to kill him. After hearing Nagisa Shiota's admission that he has the talent to become an assassin, Korosensei vows to support him despite the dangers of this path. He later disguised himself as Tadaomi Karasuma during a parent-teacher interview with Nagisa's mother Hiromi Shiota who wants to transfer her son back to the main campus. But seeing her dominant personality and inferiority complex to make Nagisa follow the path in life she laid out for him, Korosensei refuses her request. That night he saw Nagisa take out a hidden assassin in front of his mother and drove them both back to their house.

Final Battle with Chairman Asano

During the school festival, Korosensei advised the students to use the mountain to find natural ingredients to make acorn noodles to attract customers to travel the one-kilometer trek from the main campus to the 3-E classroom. In his final battle with Chairman Gakuho Asano, Korosensei aided his students to triumph over Class A and even turned the tables when Asano himself arrived to kill him. There Korosensei revealed that he based his teaching methods based on Asano's own methods in his early teaching career and was responsible for Asano somewhat regaining his former kind personality.

End of the Semester: Past Time

The end of the semester took a dangerous twist when Kaede Kayano launched a surprise attack on Korosensei, revealing to have implanted tentacles on herself. Korosensei managed to avoid falling into a anti-sensei BB-filled pit by blasting a hole in the wall, prompting Kayano to recoil on instinct. Korosensei asked what happened to her afterwards and she reveals to be the younger sister of Aguri Yukimura, drawing a surprised reaction from him and her classmates. At the students' insistence and seeing his past finally catching up to him, Korosensei agreed to tell the full story of his past, but not until Kayano is subdued.

He and the class meet her at Kunigigaoka Park and the two start to fight. Immediately, Korosensei senses Kayano's subconscious fading as her tentacles start to dominate and asks the class to find a way to calm Kayano's bloodlust before she dies. Korosensei intentionally reveals his main weak point - his heart behind his crescent moon tie - and Kayano strikes. Despite being gravely wounded, Korosensei pins her down stating his promise to her sister not to let any of his students fall, allowing Nagisa Shiota to approach Kayano and kiss her into unconsciousness. Korosensei removes her tentacles and sees Shiro (who Korosensei now recognizes to be his jailer Kotaro Yanagisawa) watching the whole thing with a masked accomplice. When Kayano woke up filled with regret, Korosensei tells the class about his past as the original Reaper, bonding with Aguri during his captivity and promising to teach her students before she died during his escape. He also stated that even if no one managed to assassinate him by March, he would die along with the entire world.

Final Semester

Division Time: The Civil War of Class E

At the start of the final semester, Korosensei greets his class with the usual enthusiasm, but he notices their unenthusiastic response even after the winter break stemming from hearing his past. While Tadaomi Karasuma is worried that their motivation to kill is weakened, Korosensei only states how the class will respond. The teachers later arrive after seeing a student meeting taking place but degenerates into a violent scuffle between Nagisa Shiota and Karma Akabane. Korosensei mediates the situation by suggesting that the two factions (those wanting to kill Korosensei and those wanting to save him) settle their differences by playing a paintball game with the winning side having their opinion to be the final say in uniting the class again.

Korosensei later watches the battle unfold from a raised platform and commentates on some of the individual students' hidden talents. When the fight is reduced to a last man standing between Nagisa and Karma, he compares each of the boys' specialized skills. Eventually, Nagisa wins when Karma surrenders voluntarily, but the class has been reunited under a common goal once more. Karasuma later speculates that the war is what Korosensei had planned all along, another lesson to educate the students.

Renewed Resolve

Searching for a way to save their teacher, the class eventually came across information that could meet their purpose. The information is based on American research data experimenting on neutralizing the antimatter without causing it to explode. However, the experiments are being conducted onboard the International Space Station by trained personnel. Korosensei suggests a crazy plan to the students to infiltrate a Japanese launch site and have two students replace the dummies in the shuttle and essentially hijack the space station. At the site, the class quietly infiltrates the facility and delegate Nagisa Shiota and Karma Akabane to be the hijackers. As the two launch into space, Korosensei barely manages to keep up with the launched shuttle as he wishes the pair luck.

The boys return to Earth with the data and Korosensei helps Ritsu steer the shuttle back to their classroom. After bribing an irritated Tadaomi Karasuma with the successful experiment of sending two living beings into space without any harm done, he soon learns from the research data that the chances of him self-destructing in March is less than one percent. Moreover, the chemical he and Manami Okuda worked on back in the first semester that liquified him neutralizes the antimatter's effects. Despite learning this, Nagisa and the class resolve to at least continue their mission to kill their teacher until graduation. Hearing this, Korosensei throws a quick-fire spontaneous round of festivities the class did not experience during the winter break due to their depressed state after hearing his past. While he celebrates, the class made numerous attempts to kill him, but their target's speed and their own sloppiness meant their efforts were for nothing. The teacher soon brings the class back down to reality by announcing the high school entrance exams in two weeks and that he will hold another careers consultation afterward to discuss the students' futures after graduation.

Return to shenanigans

When the entrance exams arrive, Korosensei wished every student good luck with his usual enthusiasm (unwittingly embarrassing them in the process). Afterward, he tried to console a devastated Kotaro Takebayashi who bombed out in getting to the top high school as his first preference. He also punished every student that uttered any words synonymous with 'fail' with an outdated hairstyle known as 'seven-three'. The class eventually realize that their target was baiting them purposefully to entertain himself and try to kill him in anger.

A day before Valentine's Day, Korosensei influences Hiroto Maehara to spend time with Hinata Okano as a way to catch more love gossip. Maehara took his advice and knew of Korosensei's motives to spy on them and had some of the class waits in ambush. This failed, but Okano was especially infuriated at not being told of this plan, making Maehara end up trying to reconcile with her the next day. Korosensei spent much of the day spying on the class for love gossip, but was easily distracted by Kaede Kayano's photo of Aguri Yukimura in a swimsuit and the chocolate present, preventing him from taking pictures of Kayano and Nagisa Shiota. During night time when he continued to admire Aguri in a swimsuit photo in the staff room, he dodged Chairman Gakuho Asano's sudden attack and was offered the choice to continue teaching after March; however, Korosensei declined, and they are chatting together for the whole night.

With the whole class having been accepted in their top preferences for high school, Korosensei wanted to collate a graduation photo album using the 10,000 photos he had already taken, most of them being the students' private or embarrassing moments. Believing this to be not enough, he then gathered the class for a quick round-the-world tour, taking snapshots and leaving without any chance for sightseeing. Afterward, he met the students individually for another careers consultation and met Nagisa last. He was happy that Nagisa decided to become a teacher and supported his decision. After Tadaomi Karasuma leaves the classroom with Korosensei compiling his graduation photo album, a weaponized beam of light struck the classroom.

Assassination Time, 2nd Hour

Much to the government's surprise, Korosensei escaped the space weapon dubbed the "Spear of Heaven" but not unscathed. He tried to fly away but was blocked by the impenetrable "Earth Shield", which also extended underground. Trapped on the mountain, Korosensei was impressed and seemingly admitted defeat. He continued to work on the graduation album though he wished to see his students one last time.

On the final night of the deadline, Korosensei and the class happily reunited. Briefed of the situation and that the satellite weapon would fire again in 90 minutes, he imparts one last life lesson to his students - to confront and navigate through society head-on and not reject it as he once did. Rio Nakamura presents their teacher with a small cake to mark the event Aguri Yukimura declared to be his birthday (the day she and Korosensei first met each other). Having not eaten any sweets for nearly a week, Korosensei starts drooling on the cake but nonetheless feels happiness. However, before he could blow out the candle, the cake was destroyed by Shiro, accompanied by Korosensei's former apprentice (No. 2), who is now a hideous tentacled monster.

The two proceed to fight where it was obvious to everyone that No. 2 could reach speeds at Mach 40 and Korosensei was barely able to defend himself. Furthermore, Shiro injected himself with a tentacle seed to become superhuman while retaining his intelligence to support the apprentice. When Korosensei began to dodge their attacks more effectively, Shiro ordered No. 2 to attack the defenseless class. As his natural duty, Korosensei took the full brunt of the apprentice's attacks to protect them and he declared that protecting them is not his critical weakness but rather the happiest gift he had been given. Korosensei continues wearing himself down to protect them until Kaede Kayano fires a shot at No. 2 to buy her teacher time to heal himself. Despite Korosensei's protests, Kayano was able to damage one of No. 2's tentacles but was pierced right in the chest, the same manner as her sister. Seeing all this, Korosensei turns black as a sign of his rage. Shiro injects the second Reaper with a needle, supposedly a stimulant of some sort, to match his power more easily. As Reaper 2.0's attack hurtles towards his 'heart', Korosensei stops it with white energy, much to Shiro's surprise. Fusing all his emotions and colors together, he uses his ranged energy explosion tactic, blasting away Reaper 2.0 and Shiro.

While Shiro humiliatingly disintegrated by the barrier, Korosensei knifed his apprentice in the chest. The two share one last exchange where Korosensei acknowledges his former student's wish and promises to start over should they meet "on the other side" before the Reaper also disintegrated. Korosensei returns to the students and starts treating Kayano's wounds, collecting her blood before the droplets hit the ground even while fighting his opponents. As the students celebrate Kayano's miracle recovery, Korosensei stares up at the night sky, wondering whether he had successfully fulfilled his promise to Aguri.

Final moments

Korosensei then collapsed out of fatigue from his fight with Reaper 2.0, and after noticing the laser's light intensifying, he announced that now was the time for the class to kill him. Once the class reluctantly decided to pin him down, Korosensei tells his students that he left them each a book of advice as a farewell gift and that he would announce one last roll call. As he calls out the list of names, he reminisces how he is proud of his students who gave meaning to his life.

Korosensei's body dissipates into yellow particles.

Nagisa Shiota, who chose to deliver the killing blow, becomes overwhelmed by his emotions. In response, Korosensei softly places a tentacle on his cheek and tells that he wants Nagisa to kill him with a smile on his face. After giving each other their final farewells, Korosensei is stabbed in the heart and his body dissipated into numerous light particles.

Powers and Abilities

As a human, Koro-sensei was a skilled assassin and contract killer. He was knowledgeable in various forms of armed and unarmed combat, planning and executing missions to eliminate targets, and various scientific disciplines to aid him in preparing for assignments. Koro-sensei gained superhuman abilities through Kotaro Yanagisawa's experiment with tentacle cells, and he has used his skills to teach and help others, and uses them to great effect as Class 3-E's homeroom teacher.

Powers

• Enhanced Strength: Koro-sensei is strong enough to lift multiple human beings with his tentacles, and knock out multiple assailants (including trained mercenaries) in a matter of seconds. However, his strength has an upper limit, and he can be overpowered if his opponent manages to secure all of his tentacles and prevent him from moving.
• Superhuman Speed and Reflexes: Koro-sensei is capable of moving at speeds of up to Mach 20. This allows him to perceive and react to incoming threats to his person (such as assassination attempts), and travel vast distances in a matter of minutes. As moving at his maximum speed would generate shockwaves which would affect those around him (including his students), Koro-sensei usually limits himself to speeds of up to Mach 3 while in the classroom.
  • Afterimage Generation: Koro-sensei's immense speed allows him to generate body doubles of himself, by moving rapidly between positions. While doing so, Koro-sensei is able to multi-task, engaging in various activities simultaneously without any trouble. For example, he was able to hold 27 different conversations and individually consult with each of his students during a test-preparation session, while having one more double taking a break outside the classroom.
  • Flight: Koro-sensei is able to fly at supersonic speeds, and can carry loads while in midair. He has been shown to be strong enough to carry the entire Class 3-E in a satchel across the world, using his tentacles to slingshot himself and the students into the air. While in midair, his head demonstrates dilatancy - becoming more solid due to the air resistance acting against him.
• Superhuman Senses: Koro-sensei's senses have been augmented by the tentacle experiments. Despite having no visible ears or nose, he is able to detect the most miniscule changes in temperature, light, sound, and smell in his surroundings. Koro-sensei can identify various things by smell, such as people, weapons, and materials such as explosives and toxic substances.
  • Telescopic Vision: Koro-sensei's vision is sharp enough to perceive objects beyond the normal range of a human being. He can also extend his eyes out of his head to zoom in on faraway items, similar to a pair of binoculars.
  • Physical Analysis: Koro-sensei's tentacles are extremely sensitive, and can analyze a person's body simply through physical contact. This allows him to understand a person's physical capabilities, potential, and limitations, and also detect any abnormalities within a person's body.
• Cephalopod Physiology: Due to the experiments conducted on him, Koro-sensei's physical appearance transformed to resemble that of an octopus. He has multiple prehensile tentacles, which he can use to grasp and manipulate objects in his environment. Two of his tentacles have small tendrils which resemble fingers, and he uses these as his hands. The rest of his tentacles are arranged beneath his body, and perform the function of legs and feet. These tentacles are extremely elastic, and can stretch to extreme lengths and form complex shapes.
  • Superhuman Dexterity: Through rigorous training with his powers, Koro-sensei has achieved extremely fine control over his tentacles. He is able to perform surgery at the cellular level, excising a malignant tumor in Azusa's brain, and healing Kaede Kayano from a mortal wound sustained while fighting against Yanagisawa.
  • Color Shifting: Koro-sensei can change the color of his skin to blend in with his environment. He usually uses this skill to disguise himself as a human, altering his skin tone so he can travel without attracting too much attention. Koro-sensei also expresses his emotions by changing the color of his head.
  • Protective Mucus: Koro-sensei secretes mucus instead of regular body fluids (such as blood, sweat, or tears). The mucus serves several purposes, such as cleansing his body of dirt and grime, and also as an adhesive.
  • Regeneration: Like a real octopus, Koro-sensei can regenerate lost limbs. He can also heal rapidly from most non-lethal injuries, although he will take longer to heal from otherwise mortal wounds.
• Nigh-Invulnerability: Due to the nature of his body and the tentacle implants, Koro-sensei is impervious to most conventional weapons or methods of injury. Only specially-made items which are designed to be effective against tentacle cells will hurt him, such as the specially made BB shots and knives used by the students, the anti-tentacle items created by Shiro, and the Spear of Heaven and Shield of Earth which were used in the Japanese government's attempt to kill him once and for all.
  • Poison Immunity: Koro-sensei can safely consume most chemicals and substances which are toxic to human beings - including concentrated sodium hydroxide, thallium (III) acetate, and aqua regia. However, his physical appearance may be affected (for example, drinking concentrated sodium hydroxide caused his head to turn blue and sprout horns).
  • Absolute Defense Form: Koro-sensei can assume this form as a last-ditch effort to protect himself from harm. He was forced to reveal this ability, after Class 3-E came exceedingly close to successfully killing him on their trip to Okinawa. In this form, Koro-sensei compresses himself into a baseball-sized crystal sphere, with his head in the centre. The energy released through compressing himself forms the crystal layer, which forms small, densely-packed matrices which are impervious to any and everything - even conventional Anti-Sensei weapons. Koro-sensei can remain in this form for a maximum of 24 hours, after which he will return to his original form. While in this form, Koro-sensei is virtually indestructible, but he is immobile and must be carried around.
  • Molting: Koro-sensei can shed his skin to use as a protective membrane - either on himself, or on another individual, to protect them from harm. He can only do so once a month, as molting tends to take up a lot of his energy.
• Energy Generation: By channeling the energy from the antimatter within his body, Koro-sensei can discharge energy beams from his tentacle tips, and even generate explosive shockwaves to destroy barriers and obstacles without touching them. He used this technique to blast away the Anti-Sensei barrier erected by Shiro to contain him.
• Superhuman Metabolism: While Koro-sensei still needs to eat and drink food, he can consume virtually anything with no ill side-effects besides items made of Anti-Sensei material. Koro-sensei especially enjoys sweets and junk food, but he will eat anything he can get his tentacles on - including non-food items such as tissues, pens, and rocks. Koro-sensei can also consume alcohol, although he has a low tolerance and gets drunk easily.

Abilities

• Genius-Level Intellect: Even before Koro-sensei gained his powers, he was extremely intelligent, able to memorize, calculate and understand vast amounts of information with exceptional precision. After gaining his powers, Koro-sensei gained the ability to think and process information at superhuman speeds, allowing him to singlehandedly teach every single academic subject for Class 3-E, craft individual tests for each of them, and even coach them one-on-one in self-study sessions.
  • Eidetic Memory: Koro-sensei has an incredibly detailed memory, and has total recall of anything he has ever seen or experienced. Before coming to Class 3-E, Koro-sensei committed all of Japan's academic literature to memory so he would be able to coach his students even better.
  • Chemistry: Koro-sensei has a expert-level understanding of chemistry, as he was able to coach his student Manami Okuda into creating an original compound which would enhance his speed and fluidity.
  • Computer Engineering and Programming: Koro-sensei was able to upgrade Ritsu's console and software, increasing her ability to interact with her classmates and aid them in assassinating him. The upgrades he installed allowed Ritsu to gain sentience and free will.
  • Pedagogy: Koro-sensei is an excellent teacher, able to consider the strengths and weaknesses of his students and teach them in a manner which allows them to grow academically and personally. He takes any opportunity he can to educate his students not just about being strong in and out of the classroom, but also about being considerate and sensitive to the people and world around them.
• Assassination Mastery: As the original Reaper, Koro-sensei was considered the world's best assassin prior to being betrayed by his disciple. Koro-sensei uses this knowledge to counter and react to every single attempt on his life, both by Class 3-E and the other professional assassins aiming for the bounty on his head.
• Driving: Despite his mutated physiology, Koro-sensei is able to drive a car. However, he dislikes driving due to it being much slower than his regular movement speed, and having to follow traffic rules.

Weaknesses

Because of his answer to the tentacles when they questioned him from within, Korosensei gained a number of weaknesses when he became the teacher of Class 3-E. Below is a list of such weaknesses recorded by Nagisa Shiota.

1. When he tries to act cool, his weaknesses show. Koro-sensei is prone to bouts of hubris - especially when he feels he has the upper hand against the students. These are the moments when he is most likely to falter and be vulnerable.
2. He is surprisingly quick to panic.
3. He is petty. Koro-sensei gave his students extra homework after their attempt to assassinate him - after he had handicapped himself.
4. His punches are soft.
5. Boobs (natural weakness). Koro-sensei is a pervert, and especially likes large breasts. He also owns a sizeable collection of dirty magazines, which he reads on the regular.
6. He is subservient to his superiors at work. When Gakuho Asano came to visit the E-Class campus, Koro-sensei proceeded to welcome him by making him tea and massaging his shoulders.
7. He has no patience for wire puzzles. Koro-sensei was unable to solve a wire puzzle when Gakuho Asano threw one at him and asked him to solve it in one second.
8. He gets motion sickness. Koro-sensei suffers from motion sickness on vehicles such as high-speed trains and ferries.
9. He can't sleep on a pillow other than his own.
10. He worries about appearances.
11. He can't handle hot food.
12. Getting wet makes him swell up (natural weakness). Koro-sensei's body is extremely absorbent, and contact with water will cause him to swell up. This affects his movement speed and reaction time.
13. Juicy gossip. Koro-sensei is especially into shipping his students with each other, and tends to spy on them whenever they discuss their romantic lives.
14. Hackneyed plot developments make him cry.
15. He gets taken in by rumors. 
16. He uses up stamina after molting, slowing him down (natural weakness).
17. He uses up stamina after regeneration, slowing him down (natural weakness). 
18. His body goes rigid when bathed in a special beam of light (natural weakness).
19. When he returns to normal after a serious situation, he gets embarrassed.
20. He can only draw simple pictures.
21. Heat fatigue.
22. He is strict about poolside manner.
23. He can't swim (natural weakness). Koro-sensei can still move in water, but he requires a full-body suit to keep himself dry. If he were to get wet, Koro-sensei's body would swell up, restricting his movements.
24. He is weak against the occult. While on Okinawa, Koro-sensei set up a test of courage inside one of the island's caves - only to end up scaring himself.
25. If he can't gather people, he feels worthless.
26. Tone-deafness. Koro-sensei is a decent singer, but he loses his tone when he tries too hard.
27. He sucks at hiding.
28. He gets carried away by official positions.
29. His heart (natural weakness). Despite being heavily mutated, Koro-sensei still retains vestiges of his former human physique, and has a heart located in the middle of his chest (behind his necktie).
30. Not related, but acts like a doting parent.
31. Gets insurance to avoid getting hurt.
32. He doesn't really know what the phrase "your own football" means.
33. He sucks at reporting. When Karasuma and the Reaper were fighting, Koro-sensei was the only one who could see them with his telescopic vision - but he was terrible at giving his students the play-by-play of the fight.
34. He suffers from road rage. Koro-sensei is used to flying from place to place, so he dislikes driving due to having to follow the rules of the road.
35. Restructuring (natural weakness).
36. He doesn’t have much brute strength, so if all of his tentacles are grabbed at once, he would be unable to escape (Natural weakness).
37. Unintentionally adding insult to injury.
38. Completely oblivious to the mood in moments of high tension.
39. Class 3-E students: Arguably Korosensei's greatest weakness. Although students of 3-E class are subtly aware of this, only three students ever made actual attempts to exploit this factor: Karma Akabane, Nagisa Shiota (using himself as bait), and Ryoma Terasaka (using Nagisa as a suicide bomber the first time, second when he was unknowingly manipulated by Shiro into nearly drowning his classmates, but has redeemed himself since). Exploiting this weakness means one has no qualms of discarding lives of his/her classmates, and even their own; Yanagisawa has demonstrated these qualities.

Foibles

Korosensei hides certain things from his students in his life, which was revealed during the extra chapters. Here are the foibles that Korosensei has for his life as an adult.

1. Painfully narcissistic designs. Koro-sensei's retreat in the mountains resembles his face.
2. His room resembles a dumpster. Despite being obsessed with grooming others, Koro-sensei's own quarters are incredibly messy.
3. He only makes petty wagers.
4. A bit of a degenerate octopus.
5. His purpose has shifted from using porn magazines to collecting them all, at this point. Koro-sensei has an entire room lined with adult magazines, and he frequently meditates in this room instead of reading the magazines.
6. Starts a night off with a Cassis Orange (a cocktail with low alcoholic content).
7. Takes forever to decide on an appetizer.
8. Really can't hold his liquor.
9. Kind of like an old geezer.

Relationships

Class 3-E

Main article: Class 3-E

In general, Korosensei has a good relationship with all his students, helping by doing anything he can. As a result, he is highly respected by them. His positive relationship with the class stems from his promise to their former teacher Aguri Yukimura to give them courage and not let any of the students fall behind.

Korosensei loves and cherishes his students and he is very protective of them that he has a tendency to get mad as seen when Ryoma Terasaka, Taisei Yoshida and Takuya Muramatsu used Nagisa Shiota as bait, Akira Takaoka kneed Hiroto Maehara and slapped Yukiko Kanzaki while revealing his plans to bury Korosensei and Kaede Kayano in cement alive.

Korosensei does not show favoritism with any student, but he is particularly interested in Nagisa for not just being quiet and well-mannered, but for his talents as an assassin, who eventually followed his path to become a teacher.

Aguri Yukimura

Main article: Aguri Yukimura

Korosensei's first impressions of Aguri were neutral, seeing her only as a means of escape but commented on her bizarre fashion sense and scatterbrain behavior.

However, as time passed, their relationship became close after Aguri taught him what "compassion was". Eventually, Korosensei finally told her of his life and Aguri expressed her desire to instill courage in her depressed students. They got closer to each other as they talked and it's implied that Aguri might harbor feelings towards Korosensei. Additionally, as the tentacles revealed its host's true feelings, it's depicted that Korosensei looked at Aguri with lecherous intent when she wore a revealing dress.

Aguri's death inspired Korosensei to take up teaching, leading to current events with Class 3-E.

In extra pages, it's shown that Aguri perceives Korosensei's new appearence with lecherous intent and vice versa. They reunited and stayed with each other in the afterlife.

The Reaper

Main article: The Reaper

His apprentice, whom he met killing his father. After witnessing the killing, the child became enamored and requested that the Reaper train him as his apprentice. Eager for the assassination opportunities that an apprentice could give, the Reaper took in the boy and trained him.

Even though he taught him everything he knew, all while still instilling respect and fear in him and letting him know the difference in power between them, the first Reaper still saw him as his tool rather than a real student, which eventually cost him his apprentice to and abandoned him at a prison after realizing his teacher's view of him.

After the Reaper was captured, he admitted to Aguri Yukimura that he was dumbfounded on why his student betrayed him, to which she responded that he might want his master to acknowledge him. Many years later, the second Reaper's wish for his master to acknowledge him still lingered even when he was given tentacles by Shiro and right before his death.

Gakuho Asano

Main article: Gakuho Asano

Initially, Asano presented himself as Korosensei's work superior and a major adversary at teaching. He made it a point to stand as a wall between Korosensei and his goals for improving Class 3-E. However, Korosensei managed to overcome those blocks. It was revealed that they share many similarities in how they want to raise strong and capable students and how they are both "monsters" that dedicate themselves to teaching.

After beating Chairman Asano, their relationship had noticeably improved; the chairman no longer stood as a barrier to Class E's growth but rather another assassin aiming to kill Korosensei. During Valentine's Day, Asano offered to allow Korosensei to continue teaching at Kunugigaoka Junior High School, something Korosensei views as a sign of great honor and respect. On that day, Korosensei had a friendly conversation with Asano and thanked the chairman for making him truly enjoy his experience as a teacher.

Their shared desire to teach ultimately results in a lot of trust between them. In the final volume, Asano is described as Korosensei's "greatest supporter" and when Korosensei reflects on which assassination attempts were the closest to succeeding, he mentions that he wasn't too worried about participating in Asano's game because he knew the explosion wouldn't be so strong as to injure the other students.

Tadaomi Karasuma

Main article: Tadaomi Karasuma

Most of the time, Karasuma seems annoyed and exasperated by Korosensei. Various students remark that, under different circumstances, they could have become close friends. It was noted that Karasuma never calls Koro-sensei by his name, addressing him as "octopus". Only during Korosensei's final moments is the only instance where Karasuma addresses his given name.

Irina Jelavić

Main article: Irina Jelavić

Most of the time, Irina tries to attack Korosensei who easily evades her attacks. Even though Korosensei constantly mocks her attempts to kill him and her love life, they have both friendly and professional relationship. Korosensei is the only one in Class 3-E addresses her as Irina-sensei (Miss Irina).

Quotes

• (His vow to Aguri Yukimura after her death) "So long as I have time... I will use this as a teacher. The students you watch over, I will watch them myself. No matter what, these tentacles will not let them go."
• (To Nagisa Shiota) "The fact that I'm targeted by everyone is proof that I'm powerful, after all."
• (To Itona Horibe) "For sensei, assassination is education. The sensei of the assassination classroom becomes stronger as he teaches."
• (To his apprentice) "My dear student... may you graduate... in peace."
• (To Gakuho Asano on Valentine's Day) "You didn't let emotions or background cloud your judgement... and evaluate me solely on my aptitude as a teacher. Such a proposal is the happiest report card you could have given me."
• (To Class 3-E after telling his past) "If I'm going to be killed, it can't be at the hands of anyone else. I want to be killed by you."
• (To Class 3-E) "As you go through life, the mighty current of society is bound to get in your way, and there will certainly be times things don't go as you'd hoped. When this happens, do not look to society for a cause. Do not renounce society. Frankly, you'd be wasting your time. Instead, just say, "That's life!" and muddle your way through with frustration."
• "The difference between the novice and the master is that the master has failed more times than the novice has tried."
• "Take advantage of what you have, while you have it."
• "The tentacles spoke to me, asked what I wanted to be. To be weak I said, to be flawed, vulnerable. To perceive weakness in others not to exploit but to protect. To be a guide, to be a teacher."
• "To kill is an action which overflows in everyday life. In actuality the more you try to be accepted, the more you kill your unrestrained self."
• "Honestly, there isn't much meaning to the splendid names given to you by your parents. What does have meaning, is what the person behind that name does during their actual lifetime. The name doesn't make the person. The name simply remains gently within the footprint left on the path a person walks."
• "You may have grown too strong. Drunk on your own power, you forgot to put yourself in the shoes of someone weaker than you. That makes you no different than the student in the main campus."
• "I’m up a creek here. That’s what everyone the world over must be thinking. But I’m a Mach-20 monster, sorry to say. And luckily for me, I have quite a bit to do."
• "If I wasn't prepared to be flexible as the situations demands, I wouldn't have become a teacher."
• "The world will always be filled with injustice. If you have time to give up or hold a grudge against that injustice, then use that time to enjoy battling those injustices instead."
• He made up his own song to teach class 3-E how to draw his face using geographical locations. Here are the lyrics "First you take the planet Earth round and blue and green, And floating over Tokyo you drop a giant bean, put another one in Sichuan China What a sheen, Taking off from Dubai to Hawaii at Mach 20 leave contours as you fly double back across the southern hemisphere over the Philippians once again to old Dubai , and then back to Hawaii drawing lines of latitude every 25 degrees along the way, and there you have it Koro se-ensei." This masterpiece is performed in Episode 43.

Trivia

• Koro-sensei likes to depict himself as an octopus. He draws himself as an octopus when marking worksheets, picks the octopus skin when he plays video games, and has a habit of burying himself up to his face in the 3-E Campus's sandbox, mimicking an octopus trap.
  • His ability to regenerate his tentacles, healing others, bestowing wisdom, and appearance is reminiscent of the Akkorokamui, a giant octopus from Ainu folklore.
• In the popularity poll in Volume 12, Korosensei was ranked 3rd.
• Koro-sensei has never actually known his birth name or his parents, due to his dysfunctional childhood.
• According to Aguri Yukimura, Korosensei is not Japanese.
• Korosensei is portrayed by Jun Fukuyama, who previously portrayed another manipulative protagonist, Lelouch vi Britannia, from the Code Geass series.
• According to his feedback for Nagisa's homework assignment on his favorite food, Koro-sensei's favorite sushi ingredient is botan-ebi, or spot prawns.