Aoi is a married woman who has been married to her husband for three years. She feels lonely because her husband's attitude is far from the kindness he showed her at first. While drowning in her worries, she goes out to buy dinner and by chance meets Hosoda, a classmate from her school days. There, she learns that Hosoda works at a swimming school and is invited to come and observe. Aoi decides to attend the swimming school. From then on, every time she attends the swimming school, Hosoda encourages her about her worries about her husband, and Aoi begins to feel attracted to him. Then, one day when her frustration with her husband explodes, Aoi crosses the line with Hosoda...