Welcome to the murderer's room. Kotaro Kuoto is a high school boy who is rumored to be the "strongest man on the street" and lives close to his sister, Hinami. One day, some thugs who had previously abducted Hinami, are found dead, and Kotaro is arrested on suspicion of murder. Despite his pleas of innocence, Kotaro is transported to a certain school as a underage murderer. What awaits him at the school are underage vicious killers who meet a special admission criteria, as well as a group of crazy teachers.