Homeroom.

Aida Rintaro is a handsome teacher who is popular among the female students. Rintaro is the homeroom teacher of a class that has a student called Sakurai Sachiko, who constantly gets bullied by her classmates. With strong sense of justice, Rintaro is always there helping Sachiko whenever she gets bullied. To Sachiko, Rintaro is like a "hero" and she starts liking him. However, unlike what's being shown, Rintaro is actually the person who planned all the bullying pranks. He pretended to be a "hero" and save Sachiko repeatedly in order to get liked by her.