After losing her husband, Yui lives alone with her son. The son is a recluse, and Yui takes care of him every day. But their relationship is more than just appearances. Even before her husband's death, they had begun seeing each other as potential lovers. Despite their roles as stepmother and stepson, their feelings for one another have steadily deepened. As tension builds to the breaking point, Yui invites her son on a hot spring trip. To transcend their roles as mother and son, and bind their hearts and bodies together. Forbidden pleasure engulfs them both, and their longing to connect turns into overwhelming desire.