Nao and her husband have been married for a few years. Her husband is becoming more distant and less attentive to her than when they first got married. Nao feels extremely lonely as her husband seems to be drifting further away from her. With her husband's birthday coming up, Nao wants to use this occasion to improve the relationship between the two of them. Wanting to look her best on that day, Nao decides to attend a swimming class advertised in a brochure. Nao is gradually drawn to the handsome and kind swimming instructor. With her husband constantly keeping his distance, not even showing up for the birthday dinner she prepared for him, Nao is deeply disappointed. Seeking comfort, Nao turns to her swimming instructor, the only one who can warm her heart at this moment...