Shota looks forward to visiting his friend Kohei’s house every week, mainly because he gets to see Kohei’s older sister, Nanami. Known throughout the neighborhood for her huge breasts, Nanami is the absolute ideal for Shota, who can’t take his eyes off her voluptuous chest. One day, while Shota and Kohei are casually talking about a sex education lesson they had at school, Nanami suddenly appears. The atmosphere shifts instantly, leading to an unexpected and thrilling turn of events.