Half a year has passed since the protagonist moved from the countryside to Tokyo for work, and he's been smoothly adapting to both his job and city life. Recently, he even started dating a younger girlfriend. Yet his relationship with his childhood friend, Natsuki Takeuchi, remains unchanged—she continues to look after him, always concerned about whether he's adjusting well to urban life and maintaining a healthy diet. One day, Natsuki comes to stay at his place for several days. They spend the evening eating a meal she prepared, reminiscing about old times, and eventually sleeping together. That night, Natsuki climbs on top of him and starts doing erotic things. Though he knows it's wrong, his cock instinctively responds, and driven by primal urges, he ends up having sex with his childhood friend.