The students of class 3-E have a mission: kill their teacher before graduation. He has already destroyed the moon, and has promised to destroy the Earth if he can not be killed within a year. But how can this class of misfits kill a tentacled monster, capable of reaching Mach 20 speed, who may be the best teacher any of them have ever had?

Earth is threatened by a powerful creature who destroyed 70% of the moon with its power, rendering into the shape of a crescent moon forever. The creature claims that within a year, Earth will also be destroyed by him, but he offers mankind a chance to avert this fate. At the class 3-E at Kunugigaoka Junior High School, he starts working as a homeroom teacher where he teaches his students not only regular subjects, but the ways of assassination. The Japanese government promises to reward with 10 billion Yen whoever among the students succeeds to kill their teacher, whom they named Korosensei (殺せんせー, lit. Unkillable Teacher). However, this has proven to be an almost impossible task, as he has several inhuman abilities at his disposal, including the capacity of moving at twentyfold the speed of sound.

Ansatsu Kyōshitsu (暗殺教室, lit. Assassination Classroom) is a Japanese shōnen manga written and illustrated by Yūsei Matsui, following the daily lives of an extremely powerful squid-like teacher and his students dedicated to the task of assassinating him to prevent Earth from being destroyed.

An anime adaptation of Ansatsu Kyōshitsu was announced by Shueisha. It is set to be screened on Jump Super Anime Tour from October 6, 2013 to November 24, 2013.

Individual chapters have been serialized in Weekly Shōnen Jump since July 2012, with bound volumes published by Shueisha. As of July 2013, five volumes have been released in Japan.