When he returns home for the Obon holiday after a long time, his family is away for work, so he ends up spending the day alone at his parents' house. He meets up with his neighbor Yotsuba again, catches up on their recent activities, and when he talks about his girlfriend, he confesses his troubles of not being able to ejaculate during sex, which leads to him practicing sex with Yotsuba. He loses track of time as he fucks her over and over again, excited by her grown-up body.