Son Wataru has a secret he can't tell anyone: while his father is away on business, he has the habit of secretly watching his mother bathe. One day, as he peered through the usual crack in the bathroom door, his mother suddenly called out, "Come on in, let's bathe together." From that moment on, the bathroom transformed into a special place for mother and son. Filled with indescribable tension and emotion, their relationship begins to evolve into something entirely new.