A few weeks have passed since Shota's wife returned to her parents' home to give birth. Shota, who had become accustomed to living with her, was beginning to feel lonely living alone. Then suddenly, his wife's sister, Yu, showed up to stay. "I was worried you might be in trouble. Can I stay over just for tonight?" Shota warmly welcomes her, but is confused by Yu's aggressive approach to him. He frantically runs into the bathroom, but Yu barges in and presses her magnificent big breasts against him...