Rin and her husband visit the home of her father-in-law, Eikichi, who is not feeling well. That night, Eikichi sees Rin masturbating, leading to an unexpected turn of events... Eikichi is concerned about the couple's sex life, and caresses his wife mercilessly in front of his son, saying, "If you take care of me, I'll teach you what sex is!" And the father-in-law's "sex lessons" escalate more and more...