Jun's mother went on a hot spring trip with her Hawaiian club friends, and his father is away on a two-day business trip, leaving Jun home alone. At that time, he receives a call from his mother's younger sister, Chiaki, who says her aunt from Tokyo is visiting and needs a place to stay because her friend canceled plans. That night, Jun unexpectedly finds himself alone with his aunt. A virgin, Jun secretly tries to peek at his aunt bathing but gets caught and is forcibly invited into the bath with her. To awaken Jun's sexual desire, the mature woman lets him touch her body and carefully teaches him how to fondle her breasts. Though gentle and affectionate, this experience becomes an entirely new kind of stimulation for Jun.