Yoshimi Miyazaki is a 38-year-old housewife married for five years. On her first sleeper train journey, she experiences sex with a man other than her husband for the first time. As the train moves forward, she carries tension and anxiety, but her sensitive body—previously restrained by masturbation—gradually responds to stimulation. Reflecting her naked body in the train window, she loses herself in passionate sex. The next morning, while washing her body in the shower room, she is stimulated by a vibrator, takes a man's penis into her mouth again, and enjoys new experiences.