A boy drowns chasing his grandfather's ghost into the ocean and wakes up face-to-face with the only person who could possibly understand what it means to not belong on solid ground. The romance that follows isn't about conquering difference, it's about recognizing yourself in someone else's strangeness. Shima doesn't save the merman or get saved by him; they just stop being alone in the wrong world at the same time.

Shima chases a photograph of his late grandfather into the ocean and nearly drowns in the attempt, since he cannot swim. A mysterious figure pulls him from the water: a handsome merman, human only from the waist up, whom Shima names Isaki. For someone who has always felt out of place, the rescue is a revelation. Seeing how shaken Shima is, the merman insists on staying at his home until he has recovered. As they spend time together, an unexpected bond forms between them, one neither of them anticipated. But romance between a human and a being of an entirely different species comes with complications, and keeping a lasting relationship afloat will not be easy.