Iori, a married woman working as an instructor at a swimming class. Her relationship with her husband has grown cold compared to the early days of their marriage, and swimming in the pool has become her only escape from daily stress. One day, her husband brings home his junior colleague, Sugimura, who begins attending her swimming class. For Iori, who usually teaches children, the muscular and rugged Sugimura becomes an unexpected thrill, awakening feelings she hasn't felt in years. Meanwhile, Sugimura can't help but see Iori as a woman when he sees her in her swimsuit, and despite knowing she's married, he gradually crosses the line.