Very Private Lesson (1988)

Tairaku is a teacher at a local high school. He has a crush on Ms. Satsuki, a fellow teacher whom he hopes to someday marry. Then he meets Aya Shirakaba, upon whom he makes such a favorable impression that she transfers into his class. Unfortunately, Aya's father is a very wealthy and powerful yakuza boss, who charges Tairaku with keeping his daughter safe and pure—or else. Add to that the hordes of men and women at school who'd love to get their hands on Aya's body, and that Aya has secretly moved in with Tairaku, and constantly makes passes at him, and Tairaku is now in world of trouble.