Sae, a mother, noticed that her son, who had recently hit puberty, was looking at her differently than before. Of course, she had repeatedly told herself it was just her imagination, but she was not satisfied... Then, one day, after getting out of the bath, Sae bumped into her son in the changing room. She called out, "What's wrong?", but noticed that her son was acting strangely, and when she looked at his hands, she saw that he was tightly clutching Sae's underwear...