Fuyuhiko has developed a hidden habit: whenever his father is away on business, he peeks at his mother, Ayumi, while she is in the bath. Unbeknownst to him, Ayumi has been aware of her son's voyeurism for some time. One evening, instead of ignoring him, she surprises Fuyuhiko by inviting him to join her. What begins as a moment of shock soon transforms the bathroom into a forbidden, private sanctuary for the two of them. The film explores their evolving, clandestine relationship through their regular bathing rituals in the steamy, intimate atmosphere of their home.