Wife "Nanako," her husband "Ryo," and their close friend "Tooru" have been inseparable since college, sharing everything with complete trust. Neither Nanako nor Tooru had ever seen each other as anything more than friends. One night, Ryo is delayed by work and returns home late. In the meantime, Tooru, eager to try out techniques he recently bought a book and hemp rope for his younger girlfriend, impulsively uses Nanako as a practice subject. Half in jest, he begins tying her up. Her bound form—accentuating her big tits and exposed thighs—draws Tooru's gaze, gradually shifting his feelings toward her. This marks the beginning of a profound change in their relationship.