Rin visits her father-in-law, Eikichi, who is unwell, with her husband. That night, Rin is caught masturbating by Eikichi, leading to an unexpected turn of events. Eikichi, concerned about the couple's sex life, brazenly caresses his daughter-in-law in front of his son, saying, 'If you take care of me, I'll teach you what sex is!' And so, Eikichi's 'sex lessons' escalate more and more...
