Chapter 1

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

Long Summary
During homeroom, in class 3-E, all the students inside were sitting in their seats nervously as the octopus-like alien creature places down a purple-blue book labeled 'Attendance' onto a table. He asks for whoever on day duty to issure the commands, and Nagisa issues a loud 'STAND!' shout, everyone in the classroom getting up with guns and shooting the alien-teacher.

The alien grins and dodges all of the bullets, calmly taking attendance of the class. Though this shocks everyone, they still went along with the attendance call. When the list was finished, the alien was happy to find that no one was absent, and by now the shooting has stopped already. The alien informs that their killing tactics are way too simple and if they wanted to kill him they need to devise a better plan. The class gets enraged, claiming that the bullets were only BB Gun pellets- and that the alien can probably endure the pain if he would feel any.

Doing a demonstration of what the BB Gun pellets can do to his body, the alien shoots his right arm off, shocking everyone, then later regenerates it. He then tells everyone to clean up the class from the BB Gun pellets. While teaching a class, as he asks Kimura a question (to which the latter answers correctly), Nagisa and Kaede tries to remember how it all began, triggering a flashback.

In the past, there were reports of the moon's 70% disappearing mysteriously, leaving only a crescent moon visible for the rest of everyone's lives. It then skips to the 3-E classroom, the alien teacher introducing himself as 'the one who blew up the moon' and their 'new teacher'. By the looks of the students at that time, it seems that no one believes the creature yet.

Karasuma, a guard from the Ministry of Defense, then tells the class their assigned mission- to kill the octopus-like creature. As everyone were shocked, Karasuma starts to explain everything that happened between the monster and them so far. He tells them that the creature plans to destroy Earth next year, at March. Karasuma takes out a blade and tries to stab the monster repeatedly, only to have him dodge every single move while hilariously in the process of trimming Karasuma's eyebrows. He reveals that the maximum speed of the octopus-creature was Mach 20, and continues explaining their objective.

MORE TO BE ADDED