Three years into her marriage, married woman Aoi finds herself growing lonely as her husband's once-tender demeanor has completely changed. One day while shopping for dinner, she unexpectedly reunites with Hosoda, her classmate from school days. Learning he works at a swimming school, Aoi accepts his invitation to visit—and immediately decides to enroll. As she begins attending weekly lessons, she gradually finds herself drawn to Hosoda's warmth and kindness. When her pent-up frustration toward her husband finally erupts, Aoi crosses the emotional boundary with Hosoda.