Fitness enthusiast Asahi learns that her adult son's friend Kentaro is out of shape and offers to train him. When she accidentally feels the size of his bulge, she remembers the lust that exercise alone cannot satisfy. Giving in to desire, Asahi plays with his cock and seduces him. But Kentaro's stamina goes far beyond one or two rounds. He makes her climax again and again until she keeps crying out in anguish, and after what feels like endless sex, Asahi finally begs him to stop.