Five years ago, when Shiori was still a student, she accidentally became involved with her younger cousin Masashi. However, it wasn't sex—they didn't go that far. Instead, she simply taught Masashi, who didn't even know how to masturbate, the basics. At the time, both were young and innocent, caught in an awkward, helpless situation. Afterward, overwhelmed by embarrassment, Shiori kept her distance from Masashi. Now, time has passed and the two meet again. But this time, Masashi is consumed by pent-up desire. The story of how he loses control, driven by lust for Shiori's body, begins here.