Asumi, whose relationship with her husband has grown cold, decides to visit her coworker Koijima's house. She feels uneasy about being alone with him, worrying how her husband might react if she doesn't return home. When Koijima confesses his feelings, Asumi accepts it as nothing more than a brief fling. Intending it to be a one-time secret encounter, she begins a special relationship with him. But gradually, Koijima's gentlemanly kindness and passionate sex start to win her heart. Before she realizes it, she finds herself thinking of him constantly and begins questioning her marriage. The story unfolds her inner transformation and the new emotions sparked by her affair with Koijima.