Kyonyû mibôjin: Yusurinaki (1991)

A woman is now a widow after her husband dies. In her prime, all she can do is pleasure herself nightly while remembering her late husband. Then, her husband's sister appears in a dispute over her husband's inheritance, claiming that she too has the right to inherit. The sister has a perverted middle-aged lover whose only purpose seems to be sex, and he breaks into the woman's house and starts having sex without her permission. Seeing this, the woman becomes even more aroused. On top of that, she is informed of a secret child that her husband had when he was young. The woman is shocked to see the child. He looks just like her late husband! The woman begins to wonder about the child..