Iori is a married woman who works as an instructor at a swimming class. - Her relationship with her husband had become colder than when they first got married, and swimming in the pool was her only way to relieve stress. - At that time, Sugimura, a junior student whom her husband brought home, ends up attending swimming lessons at her husband's recommendation. - Iori, who usually teaches c**, is conscious of Sugimura, her husband's muscular junior, as a man. - The same goes for Sugimura, who sees Iori in a swimsuit as a woman and forgets that she is a married woman, crossing the line.