The protagonist of the story is Kosuke Atami, a perverted and somewhat socially awkward teenager who reunites with his childhood friend, Shizuka Himenoki, who has transformed from a sweet little girl into a strong-willed young woman. Kosuke and Shizuka made a promise to each other as children, and while Kosuke considered it just a game, Shizuka takes it completely seriously and remains romantically interested in him. Meanwhile, the protagonist engages in sexual encounters with other classmates without paying much attention to Shizuka, but as the story progresses, their relationship gradually grows closer.