Aoi, a woman who has been married to her husband for three years. Away from her original kindness, she feels lonely in front of her husband's attitude. When she goes shopping for dinner with her worries, she happens to meet Hosoda, her classmate when she was a student. There, she learns that Hosoda is working in a swimming class, and Aoi is invited to visit her and decides to go to her swimming class. After that, every time she goes to the swimming class, Aoi begins to be attracted to Hosoda's kindness, which cheers up her husband's worries. And on the day when her dissatisfaction with her husband explodes, Aoi crosses the line with Hosoda.