Korosensei

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

Appearance
Korosensei has the appearance of a squid, he is quite tall, he has a large bulb head with a large smile and tiny beady eyes. He uses two feelers, as arms, with two fingers and use the rest to walk with them. He wears a black academic dress, a small black square academic cap with a yellow tessel, a black tie with a yellow crescent-shaped moon on it.

The color of his face varies based on his mood. His face is black when he is extremely angry. When he is neutral, his face is yellow. When a student of his gets an answer wrong, he has an X over his face, and when a student gets a question right, he has a circle over his face. He wears a graduation uniform, and has eight tentacles.

History
Korosensei was born and raised on Earth. However one day there was an accident on a school where a teacher got injured, she asked him to teach the children, while thinking how of 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 class 3-E. The world leaders accept the deal, hoping it would give them a chance to assassinated Korosensei, but also added another condition - that he would not harm the students.

Later Korosensei came with Karasuma, from the Ministry of Defense, in front of Class-E and introduced himself. Karasuma explained the situation and demanded the students to assassinate the new homeroom teacher, and tried to assassinate Korosensei himself, but Korosensei used his mach 20 speed to dodge Karasuma strikes and trimmed his eyebrows. After that, Karasuma revealed that the reward for killing him would be 10 billion yen, but Korosensei just 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
Korosensei starts the attendance, he also 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 absents, he was also ashamed that nobody could hit him. He teaches them that the should devise a plan together. The students complain that even if he would get hit by the BB pellet bullets, he would just endure it. Korosensei demonstrates that that BB bullets, created by America specially for against 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 looks down on, telling that they are 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, which Korosensei is then pleased with his correct answer. He then catches a bullet with his chalk, he becomes red and punishes Nakamura that her assassination meddles with her study. When lunchtime starts, Korosensei decides to go to China, while grading his student's their tests. Korosensei later came back with a missile souvenire after having been ambushed by the self-defence in the sea of Japan. nagisa asks him that it was troublesome that he was targeted, but Korosensei tells her that he doesn't mind and shows the vast proof of his power.

The class starts again, Korosensei decides to write a poem and the one who is finished should bring it to him. Korosensei was asked by Kayano what name they should refer him to, Korosensei tells her that they can decide. Korosensei sees Nagise walking up deliver the letter, he was suddenly striked by him, but easily blocked it. However Nagise retaliated with a BB pellet grenade, much to Korosensei surprisement, however Korosensei uses his shed skin to protect him and Nagise, which he can use once a month. After revealing his ability, he turned black with extreme anger, he called out the ringleaders of the BB pellet grenade. Korosensei roams around town with extreme speed and brought the nameplates of their houses. He tells the students, due to the agreement to not harm the students, that if they try the same assassination method that he would anihilate anyone they know. He was questioned by Terasaka of the degree of the assassination, Korosensei corrects him by saying that it was an excellent and praises Nagise for keeping a natural body movement. However Korosensei gets angry saying they held no regard of Nagise's life. He then advices that they should use an assassination that will make everyone happy and that they have hidden talents. After seeing a burn mark on a table he remembers the accident. Korosensei then asks what will they do before he blows the Earth up, nagise responds that they will kill him, Korosensei gets green stripes on his face telling that they can go home if they succeed to kill him now. After that, Kayano says what name she thought of sensei: Korosensei.