Korosensei

"Nurufufufu~"

- Korosensei's trademark laugh

Korosensei is the homeroom teacher for Class 3-E of Kunugigaoka Junior High School, and the central character and main antihero of Assassination Classroom. Korosensei claimed to be responsible for creating the permanent crescent moon and said that he plans to destroy the earth after "teaching" Class 3-E for a year.

Prior to being a teacher he was the master assassin known as the "God of Death."

Appearance
Korosensei has the appearance of an octopus. He is about three meters tall, and has a large, bulbous head with a large smile and small, beady eyes. He uses two feelers as arms, with two fingers each, and uses the rest of his tentacles to walk with. He wears a black academic dress, a small black square academic cap with a yellow tassel, and a black tie with a yellow crescent-shaped moon on it.

The color of Korosensei's face changes depending on his mood, and is as follows:
 * Yellow/Green = Happy, Emotionless
 * Yellow and Green Stripes = Mockery
 * Orange with a Red Circle = Correct Answer
 * Purple with a Dark Purple X = Incorrect Answer
 * Pink = Sleepy
 * Purple = Shock/Panic
 * Blue = Sadness
 * Red = Anger
 * Black = Extreme Anger

As a human he had black hair that reached to his nape and dark eyes. He was notably attractive and was described as having a smile kinder than anyone else.

Personality
Korosensei is very smart to the point that he can teach almost every subject by himself. He loves sweets almost extreme cases and is also shown to be a very perverted character, a trait he shares with his student Okajima. He is also rather kind, and can switch from silly to serious on the fly.

One of Korosensei's attributes is the fact that he is able to connect to each student individually. This is the reason why all the students respect him despite the fact that he is going to blow up the Earth in a year.

According to Aguri Yukimura, if he was born in a peaceful country, his personality would be "someone a little perverted, with a good head but a few screws loose, petty about small things, and also a lot stubborn... or something like that." He has/would have "a gentle smile not just for business, he is a gentle person himself."

Etymology
His name, Korosensei, is a combination of the words 殺せない (korosenai) which means "unkillable" and the word 先生 (sensei) which means teacher. It was given to him by Kaede Kayano.

History
As a child, he was born into one of the most vile and corrupt slums in an unknown country. It was an environment where everyone could easily betray you to the point that you could only trust yourself. Through these hardships, he decided to become an assassin and became the master assassin known as the God of Death. 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.

All this changed after assassinating a wealthy businessman and father. The man's child witnessed the killing and the child became enamored with the beauty of the kill and requested that the God of Death train him as an apprentice. Eager for the assassination opportunities that an apprentice could give, the God of Death took in the boy and trained the boy. He taught him everything he knew all while still enlisting respect and fear in him and letting know the difference in power. After several successful jobs, the apprentice turned on the God of Death as he was attempting to escape a prison facility. The apprentice, now the current God of Death, sought his master's title and abandoned him just to fuel his ego. Betrayed, the God of Death was captured and thrown into an undocumented research laboratory run by Kotarō Yanagisawa. Yanagisawa's research goal was to create large amounts of 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 at the time in an arranged and abusive marriage to Shiro. Aguri was brought in to keep a closer eye on the him as Yanagisawa considered her easily expendable if he attempted to break free and take her hostage. As the tests continued, the God of Death 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.

However, a problem arose when Yanagisawa and his researchers began to question 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 rat). When the rat did die at the end of its lifespan it caused a volatile reaction with the antimatter in it's body. The antimatter created a chain reaction that turned 70% of the moon's matter into antimatter, which then completely exploded. Upon seeing this, Yanagisawa was horrified at the results. His subordinates then began running calculations and discovered that the same thing will happen to the God of Death by March 13 of the following year. Earth would be destroyed the same way if left unchecked, prompting Yanagisawa to order his subordinates start preparations to kill him. A mortified Aguri overhears this and decides to go speak to the God of Death and tell him their findings. When she does however, he reveals 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 God of Death then proceeded to rampage violently, killing off several guards and in the process damaging Yanagisawa's left eye. However, during the escape Aguri is mortally wounded when she lands in the line of fire of a special tripmine meant for him to the latter's horror. He then laments the fact that if he hadn't wasted his skills on killing, he would know how to save her.

Aguri's final wish to him was to teach the students of Class E all while thinking of what a wonderful teacher he will be. With this, she also left a large tie as a present for him to take. Depressed but not broken, the God of Death vowed to help those children. He left a note then left the facility for a nearby mountain. He then uses 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 takes the blame and tells the world's leaders that he will 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 accept the deal, hoping it will give them a chance to assassinate him; however, they also added another condition: he would not harm the students.

Introduction: Assassination Time
As Korosensei starts the attendance, he asks the one who is on day duty to issue command. Korosensei was then ambushed by his students with automatic rifles; however he dodges the bullets while doing the attendance. Korosensei is pleased that that there are no absentees; 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. He warns them not to use them indoors except for killing him. He then tells them that they will be able to kill him before graduation, and decides to tidy the class up.

Later he questions 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 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 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 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 striked by him, but he easily blocked it. However, Nagisa retaliates with a BB pellet grenade, much to Korosensei's surprise; however 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 anihilate anyone they know. He was questioned by 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. Korosensei then asks what they will do before he blows the Earth up, and Nagisa responds that they will kill him. Korosensei gets green stripes on his face, telling them that they can go home if they succeed in killing him now. After that, Kayano says the name she thought of for sensei: Korosensei.

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 Gakuhu 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. 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 outmanoeuvres 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 Nakamura, Isogai and Okuda scored first place in English, Social Studies and Science respectively. However Korosensei has been conned to have four additional tentacles destroyed when Terasaka, Hazama, Muramatsu and 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 Chiba and 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 and Kayano to the mountain hotel in exchange for the antidote. Although unable to move, Korosensei assists the 15 remaining students to infiltrating the hotel, and even helped call out commands while simultaneously distracting one of the hired hit men. When the class discover the mastermind to be 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 Karasuma to intervene should anything bad happens. Fortunately Nagisa was able to defeat Takaoka and the ill students had never been in any danger; the virus being 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 organised a Test of Courage. It is supposedly 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 later half of the pairs instead turned the tables on their teacher by making him scared.

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 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 in 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 of the sceptical students find the culprit to be Shiro and Itona, who once more ambush him using the same strategy employed by Class 3-E during the summer vacation. This time, Korosensei was able to convince Itona to join them after the latter was coldly abandoned by Shiro for the repeat failures, and removed the tentacles from him.

Unwanted attention
As the mid-terms approached, some of the 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, the result that the class except for Karma dropping in rank.

The students' actions had also attracted the attention of the professional hit man known as the God of Death. 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 Karasuma defeated the God of Death.

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'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 Karasuma during a parent-teacher interview with Nagisa's mother Hiromi 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 as a way to attract customers to travel the one kilometre trek from the main campus to the 3-E classroom. In his final battle with Chairman 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 in 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. Although being gravely wounded, Korosensei pins her down stating his promise to her sister not to let any of his students fall, allowing Nagisa 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 God of Death, bonding with Aguri during his captivity and promising to teach her students before she died during his escape. He also stated that if no one managed to kill by March, he will die along with the entire world.

Division Time: The Civil War of Class E
At the start of the final semester Korosensei greets his class with usual enthusiasm. But he notices their unenthusiastic response even after the winter break stemming from hearing his past. While Karasuma is worried that their motivation to kill is weakened, Korosensei only states of how the class will respond. The teachers later arrive after seeing a student meeting taking place but degenerates into a violent scuffle between Nagisa and Karma. 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 the last man standing between Nagisa and Karma, he compares each of the boys' specialized skills.

Weaknesses

 * 1) When he tries to act cool, his weaknesses show
 * 2) He is surprisingly quick to panic
 * 3) He is petty
 * 4) His punches are weak
 * 5) Boobs
 * 6) He is humble and subservient to his superiors
 * 7) He has no patience for wire puzzles
 * 8) He gets motion sickness
 * 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
 * 13) Juicy gossip
 * 14) Hackneyed plot developments make him cry
 * 15) He gets taken in by rumors
 * 16) Time right after molting
 * 17) Time right after regeneration
 * 18) His body goes rigid when bathed in a special beam of light
 * 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's strict about poolside manner
 * 23) He can't swim
 * 24) He likes to gossip
 * 25) He is weak against the occult
 * 26) If he can't gather people he feels worthless
 * 27) Tone-deafness
 * 28) He sucks at hiding
 * 29) Gets carried away by official positions
 * 30) Heart
 * 31) Not related but acts like a doting parent
 * 32) Gets insurance to avoid getting hurt
 * 33) He doesn't really know what "your own football" means
 * 34) He sucks at reporting
 * 35) He suffers from road rage
 * 36) Restructuring
 * 37) Grabbing all his tentacles at once makes him unable to move

Class 3-E
In general, he has a good relationship with all his students and is highly respected by them.

Gakuhō Asano
Initially, the Chairman presented himself as Korosensei's superior and a major adversary. He made it a point to stand as a wall between Korosensei and his goals for improving Class 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. In the end, Korosensei performed "maintenance" on the chairman and as of Chapter 126, their relationship is noticeably better with the chairman no longer standing as an adversary to him.

Quotes

 * (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"

Trivia

 * His motto is "Learning and killing are of one body."
 * Korosensei appears as a playable character in the video game J-Stars Victory Vs.
 * He was called "Stupid Chicken Pervert Octopus" during class 3-E training using code names.
 * In the popularity poll in Volume 12, he was ranked 3rd.
 * When his tentacles asked him what he wanted, Korosensei's response was: "I want to be weak."
 * His necktie is a present from Aguri Yukimura . Though, the crescent moon motif is his own design.
 * According to Aguri, Korosensei is not Japanese.

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