Masahiro Hisano

Here, we see Sei, a very sexually advanced for his age grade-school boy, who chases and attempts to bond with cute and exciting Nao, the ultimate girl of his dreams who is in junior high and is two years older than he... (IMDB Comments)

Kenji has a hard time being intimate with his girlfriend Noriko partially because he fears he has an STD. In order to get tested, Kenji is hired by his mother to spy on his father to see if he is still cheating on her. He is, and his father's girlfriend actually starts working for the family.

Kanzen naru shiiku Meido for you: The seventh film of The Perfect Education series tells the tale of a man and a girl who pursue love to the point of madness. (letterboxd)