After several years of marriage, Hibiki has been working hard to be a ``good wife'' to her husband, but the distance between her and her husband has only grown wider, and she is worried about how she can return to her normal life. One day, Hibiki meets Aoi, the husband of Hibiki's friend who lives in her neighborhood. As they talk about their troubles, the two of them grow closer and he commits infidelity for the first time in her life. However, Hibiki doesn't know that the cost of her first affair (Kaikan) after getting married is too great...