Koakuma Kyoushi Psycho

When a high school teacher was hospitalized due to bullying by students, a new teacher is assigned to replace him. The substitute teacher Ms. Kasai is a beautiful woman, with a stunning figure. On top of that, she doesn't get bothered by risqué remarks, always responding with a smile. Even as she laughs and says, “I became a teacher to make my students happy,” her students are already making evil plans. But what the bullies don’t know — is that Ms. Kasai is a psychopath.

(Source: Peep, translated)