Korosensei

Korosensei (殺せんせー, Korosensei) is the homeroom teacher for class 3-E of Kunugigaoka Junior High School, and is the main antihero of Assassination Classroom. He is responsible for carving out a large chunk of the moon to make it a permanent crescent moon, and plans to destroy the earth after teaching class 3-E for a year.

Appearance
Korosensei has the appearance of an octopus. He is quite tall, and has a large, bulbous head with a large smile and small, beady eyes. He uses two feelers as arms, with two fingers to 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 tessel, 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
 * White and Green Stripes = Mockery
 * Pink with a Red Circle = Correct Answer
 * Purple with a Dark Purple X = Incorrect Answer
 * Pink = Love/Lust
 * Purple = Shock/Panic
 * Blue = Sadness
 * Red = Anger
 * Black = Extreme Anger

History
Korosensei was born and raised on Earth. However, one day there was an accident in a school in which a teacher became injured. The teacher asked him to teach the children, all the while thinking of what a wonderful teacher he will be.

A year before the start of the series, Korosensei destroys 70% of the moon, forever leaving it in a crescent shape. Korosensei reveals to the world's leaders that he has decided to destroy the Earth as well next year during March. He then tells the world leaders that he wants 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 Korosensei; however, they also added another condition: he would not harm the students.

Later, Korosensei came with Karasuma, whom was from the Ministry of Defense, to the front of Class-E and introduced himself. Karasuma explained the situation and demanded the students to assassinate the new homeroom teacher. As an example, he tried to assassinate Korosensei, but Korosensei used his mach 20 speed to dodge Karasuma's strikes, and even meticulously trimmed his eyebrows. After that, Karasuma revealed that the reward for killing him would be 10 billion yen, and Korosensei simply looked down on them while his skin color changed to green. After Karasuma ended his explanation and showed the weapons, Korosensei declared that they should spend the last year in a meaningful fashion.

Plot
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 the 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 that BB bullets, created specially by America for harming him, are harmless to the students, but not to him 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 her 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 gets angry, saying that they held no regard of 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.

Weaknesses

 * 1) His weaknesses show when his tries to act cool
 * 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

Quotes

 * (To Nagisa and Sugino, Chapter 21) "The amount of money in sensei's wallet is 5 yen!!"