When a picture of his late grandfather falls into the ocean, Shima jumps in after it without thinking. Nearly drowning, he is saved by a very perfect stranger - the young merman Isaki. Shima and Isaki quickly bond in ways neither anticipated. After all, Shima and Isaki aren't just from opposite sides of the tracks but from entirely divergent species, which makes maintaining a long term relationship anything but easy sailing.
Lonely Shima has always felt like a fish out of water, but when he's saved from drowning by the merman Isaki, he finds a friend who can finally understand him. But are they truly just friends, or is there something more between them?