Riina, 10 years old, secretly embarks on a trip to commit incest with her younger sister behind her parents' backs. (IBW-376)

A forbidden physical relationship between blood-related siblings. The brother and sister are alone in a secluded hot spring inn, unknown to anyone… Upon arriving at the inn, the brother's unusual sexual desire is immediately released on his sister, his accumulated semen being poured into her body in large quantities…