Koakuma Kyoushi Psycho (taskey STUDIO)

Koharu Kasai, a beauty with an incredible figure, is assigned as the new replacement teacher after the main high school instructor was hospitalized due to relentless bullying from the students. Though she appears airheaded and constantly wears a bright smile, the students continue to mistreat her, unaware of the dark secret that their teacher, Kasai-sensei, is a real psychopath. Source: MU