Four years have passed since Yukari remarried her current husband. She was worried about her husband's relationship with her stepchild, Kosuke. Her suspicions only grew as Kosuke showed signs of being aware of her as a woman, even though she was a stepmother, and her underwear was sometimes stolen while she was bathing. One day, when she entered Kosuke's room, she witnessed him trying to masturbate with Yukari's underwear. Yukari confronted him, but Kosuke ended up attacking her instead...