Season 1

In a hotel for their anniversary, Ichiko makes an advance on her husband. However, she is shocked when Otoya rejects her because of his mistress, Mitsuki. Although Ichiko permitted his affair, Otoya's rejection leaves her confused and hurt. Seeking advice from her friend, Ichiko is reminded that she is also allowed to have an affair. So she turns to an old college friend to fulfill her desires.

Ichiko finally opens up to Otoya about her painful past when they visit her mother. A few days later, Mitsuki warns him they need to be more secretive with their dates because her husband had seen them together. Mitsuki becomes angry when Otoya reveals Ichiko knew about her all along. Meanwhile, Ichiko visits a secret brothel for women and finds herself charmed by the young Rei.

Ichiko's intimate session with Rei is unfortunately cut short when she rushes home to nurse an injured Otoya. Her guilt nags at her as she cannot stop herself from thinking about Rei. Otoya promises to spend a special night with Mitsuki, breaking his and Ichiko's rule for keeping his home life and affair separate. Enraged, Ichiko quickly makes another appointment with Rei.

After not having sex for two years, Rei's gentle caresses and tender kisses move Ichiko to tears. Meanwhile, Mitsuki faces a bleeding Otoya in a hotel room. Infuriated by Otoya's refusal to sleep with her because of Ichiko, Mitsuki had impulsively stabbed him. Hurt and in shock when she learns why he was attacked, Ichiko finally confesses her true feelings about their special arrangement.

Ichiko and Otoya decide to rekindle their sex life, but their excitement quickly turns into frustration. Otoya is haunted by Mitsuki's curse-like words of goodbye and Ichiko cannot stop comparing him to Rei. When he happens upon Ichiko and Rei together, Otoya finally learns that Ichiko had paid Rei for his services. Unable to contain his disdain, Otoya blows up at Ichiko.

Mitsuki learns she is pregnant and tells Shiro he is the father. Despite his misgivings, Shiro still loves Mitsuki and attempts to change for the sake of their marriage. Since Otoya moved out, Ichiko realizes how much she came to depend on him as she comes down with a severe cold. Otoya rushes home to care for her and they make up, but unaware of all this, Rei confesses his feelings for Ichiko.

Ichiko and Otoya decide they want to have a baby. They start fertility treatments, but the stress and repeated failures take a toll on Ichiko. She finally confesses to Otoya that she is unable to picture a future with him without children, so they decide to get a divorce. Months later, the sudden death of Ichiko's mother unexpectedly brings her ex-husband back to her side.