Hinami begins living with her daughter and son-in-law, warmly accepting their household. However, the son-in-law becomes obsessed with her obscenely large breasts and harbors lustful desires. One day, he catches Hinami masturbating and discovers her sexual frustration. In that moment, he taunts her with, "You want sex, don't you?"—marking the beginning of an illicit affair. While the family is out, they have sex in the living room; during family gatherings, he secretly trains her with a vibrator under the table; in the kitchen, she performs blowjobs and titty fucks on him. As night falls, she approaches him dressed in erotic lingerie, engaging in forbidden intercourse. Betraying both his wife and deceiving the father-in-law, Hinami and her son-in-law indulge in each other's bodies daily. Their taboo relationship, crossing the boundaries of family, continues without end.