Sayo Akagi, 50 years old. Lives with her husband and son. Her husband works late every day due to overtime, and her son often stays out until late at night. With no household chores to burden her, she's been living a carefree life. But one night, she discovers her son masturbating with her underwear in the changing room. Unaware of her presence, as she stands there in her undergarments preparing dinner, her son suddenly approaches her from behind...