Assassination Classroom

This is the story of a young man who, after realising that his teacher's lesson plan is to kill him and the 25 people closest to him, decides to fight back and turn the tables on his murderous teacher. Surprise! That was the same as a manga or anime in which the protagonist, Koro-sensei, is an alien who has come to Earth to prepare it for annihilation. A teacher who looks like a chibi and gives life lessons to his students by assassinating famous historical figures.