Kono Danshi, Ningyo Hiroimashita.

A boy named Shima dives into the ocean to retrieve a photo of his late grandfather, nearly drowning in the process. He is rescued by a man who is human only from the waist up. Shima, who often feels out of place, forms a close connection with the merman, named Isaki. Their relationship, however, faces challenges due to their differences in species and backgrounds.