Married Ibuki joins a personal swimming school to improve herself while trapped in a sexless marriage. There she meets instructor Tanaka, an athletic man whose huge cock she cannot get out of her mind. While her husband is away, the faithful wife crosses the line and begins a physical relationship with the coach. Pressed together in their competition swimsuits and slick with sweat, they fall into increasingly sordid affair sex, with Tanaka pounding and creampieing her as she discovers pleasure her husband no longer gives her.