Korosensei is a teacher for class 3E of Kunugigaoka Junior High School and the main antihero of Ansatsu Kyoushitsu. He claims responsibility for blowing up the moon into a permanent crescent shape and plans to destroy the Earth in a year after teaching the students of class 3E the art of assassination. His name comes from korosenai meaning cannot be killed and sensei meaning teacher. In this way he is literally called the unkillable teacher.