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1122 いいふうふ
网页设计师的妻子相原一子和在文具制造厂工作的丈夫相原二也即使无性婚姻、没有孩子，夫妻关系也非常和谐，但是两人有秘密——每个月的第3个星期四晚上，二也会和“恋人”一起度过，结婚第7年的两人选择的是“婚外恋爱许可制”。
庆祝结婚周年在旅馆留宿时，一子向丈夫二也求欢。二也因为情人美月的关系，拒绝了一子，这让一子非常震惊。虽然这段婚外情是一子同意的，但二也的拒绝仍然让她感到伤心困惑。一子向朋友寻求建议，进而意识到她也有发生外遇的权利。于是她找到一位大学同学，来满足生理需要。
探望母亲时，一子向二也讲述了自己童年的痛苦经历。几天后，美月提醒二也在幽会时要更加小心，因为她的丈夫看到了两人在一起。二也告诉美月，一子知道两人的婚外情，这让美月非常生气。与此同时，一子去了一家以女性为服务对象的地下风俗馆，被年轻的礼迷住了。
一子和礼的亲密时光被中途打断，因为二也受了伤，一子要赶回家照顾。一子因一直想着礼，所以备受愧疚感折磨。二也答应美月，要和她共度一个特别的夜晚，这打破了他和一子不能把婚外情带回家的约定。一子一气之下，再次约礼见面。
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.
