Kasai Koharu, a beautiful girl with an exceptional sense of style, is assigned as the new replacement teacher after the main high school instructor was hospitalized due to relentless bullying from the students.
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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.
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“The reason I became a teacher is to bring happiness to my students.”