Groper Train: Finger Bullying (1996)

Ryoko is a high school girl who attends a prestigious private high school in Tokyo. However, her grades are steadily declining. Her day begins with an encounter on the train to school. It is not just the man that keeps Ryoko from studying. Ryoko's sister and her husband, Shunichi, are impotent, which makes her sister Misako sexually frustrated, and the consequences of this fall on Ryoko. The only thing that helps her relieve such stress is the man's fingers on the train to school.