Six months after getting married, Yuna's father-in-law suddenly dies. Yuna moves in with the Shoda family to take care of her mother-in-law, Chisato, who lost her husband. The bizarre behavior of the mentally unstable Chisato is beyond Yuna's imagination, and it escalates day by day, with her incontinence, wandering around, and lying. One day, Yuna can't stand to see Chisato masturbating alone, so she tries to stop her, but she is mistaken for her late husband and raped. From that day on, her lesbian training begins... but Yuna has no way of knowing that it is Chisato's obscene desire that she has forgotten...