The three of them decide to go on a trip to Izu together with Nana, a new mother-to-be introduced to them by her father. While her father is not looking, he plays pranks on Nanako as Nanako sleeps on the train. He rubs her breasts and lifts her skirt to see her panties. When they arrive in Izu, the three go to a museum together, but while her father is engrossed in looking at the exhibits, he plays pranks on her, causing trouble for her. At the inn, her son massages Nanako's stiff shoulders. However, his hands gradually slip into a sensitive area... Eventually, despite being a mother , Nanako gives in to pleasure and has sex with her son. While her husband is not looking...