Maria, who married her childhood friend Tohru, finds her marital sex life unsatisfying and begins indulging in frequent masturbation, reveling in her voluptuous body. Her ordinary routine takes a dramatic turn when her husband's older brother, Hiroshi, returns from overseas and moves in as a lodger. Recalling the guilt and simultaneous pleasure she felt as a child, Maria immerses herself in self-pleasure. Yet she grows anxious—what if Hiroshi discovers her secret? Despite her unease, Hiroshi begins giving her bold, suggestive touches, smirking in a way that blurs fantasy and reality. His words and actions slowly pull Maria into a thrilling new experience.