Chapter 1

Assassination Time (暗殺の時間, Ansatsu no jikan) is chapter 1 of the Ansatsu Kyōshitsu manga.

Short summary
A new alien teacher begins his homeroom class at Kunugigaoka Junior High School with students firing BB guns at him. The students are distraught to find the teacher unharmed.

It is revealed that just before teaching the class, the alien managed to carve the moon to become a permanent crescent moon. With his superhuman powers, he had effectively taken over the world and plotted to destroy the Earth in a year. However, he also promised the governments of the world to teach a certain class of students in the meantime without harming the students. At the same time, the Ministry of Defense, under Karasuma, promised the students a 10 billion yen reward if they can assassinate their teacher before he destroys the Earth.

At lunchtime, the alien teacher zooms off to Sichuan province in China to have some mapo doufu. Back at school, Terasaka and his friends pressure Nagisa with their own method to kill the alien teacher for money.

After lunch, Nagisa approaches the alien teacher to explode a BB pellet grenade on him successfully, as planned by Terasaka. However, the alien teacher survives anyways. He collects the nameplates of all the students' houses and threatens to kill everyone's family relatives. In the end, he praises Nagisa for his efforts but scolds Terasaka and his friends for disregarding Nagisa's safety. Kayano finally thinks of a name for their teacher, Korosensei, the unkillable teacher.