Satsuki begins an affair with Kenji, a man she met at her part-time job, separating from her husband. They agree on two rules: Satsuki will initiate all contact, and they must always use condoms during sex, maintaining their secret relationship. One day, while her husband is away on a business trip, the two head to a hot spring inn. Under the dappled sunlight, they openly hold hands and enjoy their date, filling Satsuki with genuine happiness. However, a new determination begins to grow in Kenji's heart. Unwilling to let Satsuki go, he resolves to break their rule and creampie her, introducing a forbidden desire that will ripple through their relationship.