Five years into her marriage, Kyoko lives a quiet and peaceful life with her husband. However, she has one lingering issue: living with her taciturn father-in-law. Unable to bridge the emotional gap between them, she grows frustrated with her own helplessness. Then one day, when her husband is due home late, she hears her father-in-law calling out to her from the bathroom. "Kyoko, could you wash my back?" Pleased by the simple request, she doesn't realize this small moment will mark the beginning of the end for her peaceful life—soon, their cohabitation takes a dark, lustful turn as the lewd father-in-law begins sexually harassing his daughter-in-law, awakening forbidden desires in both.