After injury and setbacks, former swimmer Anna returns to her hometown. Sharing a home with the unfamiliar Deok-hyun and reconnecting with an old friend, she finds her once-stalled life quietly beginning to move again.

Anna sets out to learn diving from Deok-hyun, a Diver. As she confronts the sea's unforgiving nature, she's pushed beyond her limits. Amid the struggle, a subtle new rhythm begins to form between them, growing with each challenge they face together.

The diving lessons begin in earnest, and though still clumsy, Anna pushes forward one step at a time. As she struggles to find her rhythm in the water, Deok-hyun guides her with a quiet, steady presence, seemingly indifferent yet gently attentive. Between them, an unspoken shift begins to surface, and the air around them starts to feel just a little different.

Back in her hometown, the afterglow of Anna's first dive still lingers in the air. As she and Deok-hyun grow closer through shared time in the sea, an unexpected sense of comfort begins to form between them. But just as things start to settle, unsettling rumors about Deok-hyun resurface, quietly disrupting the calm rhythm of their once peaceful days.

Anna uncovers a secret that should never surface, while Deok-hyun is forced to face a past he can no longer turn away from. As they confront their own limits, both are tested on whether they can find the courage to begin again.