A married woman Nao who has been married to her husband for several years. She had grown colder than at the beginning of her marriage, and she felt lonely at her distance from her ever-separating husband. In an attempt to repair her relationship with her husband, Nao plans a dinner for her husband's birthday. Nao, who wants her to look as beautiful as possible, decides that a leaflet for her swimming class catches her eye. In her swimming class, Nao gradually becomes attracted to her kindness, which is different from her instructor, Yuki's husband. And she has no way of knowing that swimming lessons for her husband will drive the couple crazy...
