A special project centered on incest unfolds. The client desires sexual relations with a family member, prompting GOS staff to take action. Eight months after viewing footage of a mother and son's incestuous encounter, the brother of the woman involved seeks revenge against his younger sister—an honor student unlike himself—and enlists Director Koki's cooperation. He instructs them to arrange a hot spring modeling gig for his sister. On the shoot day, a surprise setup brings the estranged siblings together, with the male model revealed to actually be her brother. Filmed at a hot spring inn in the style of an illicit couple, the scene gradually turns sexual. Initially repulsed, the sister slowly grows intrigued as her brother touches her. Deep down, she had always admired her brother, and upon touching his penis, she feels it deeply in her body.