Aku no Kyouten

Aku no Kyouten (悪の教典, lit. "Lesson of Evil"), also known as Lesson of the Evil, is a 2012 Japanese slasher film directed by Takashi Miike, starring Hideaki Itō. It is an adaptation of Yusuke Kishi's 2010 novel of the same name.

Plot
Hasumi Seiji, who teaches English at a high school, is affectionately known as "Hasumin" by his students. He's popular, good-looking, kind to everyone, and efficient at teaching and solving problems. But no one knows that he's actually a manipulative serial murderer. He treats the school as a kingdom he rules. He manipulates others into trusting him and obeying him. But when there are people (students, teachers and parents) who cannot be reformed, he kills them off without mercy. Eventually, his targets include all the students in his class.