Inbo no seikyôiku: Okumade chôdai (2006)

Miyuki is married to a man who has a son named Kazuya—a young man currently studying for university entrance exams. One night, while Miyuki is masturbating in the bathroom, she catches a glimpse of Kazuya on the other side of the changing room. A few days later, she spots him in a park restroom, pleasuring himself while calling out her name...