Due to her father's remarriage, Miina Wakatuki becomes the new stepmother in the Wakatsuki household. Eager to build a good relationship with her stepson, she diligently takes care of the housework. However, her son feels awkward around her and struggles with how to act. One day, with the father away on business, Miina finds her pent-up desires overwhelming. Alone in the bathroom, she soaks in the bath and begins pleasuring herself. Lost in ecstasy and oblivious to time, she is suddenly caught in the act by her stepson who stumbles upon her by chance.