MOON CHILD (Tsuki no Ko), by Reiko Shimizu. First published in 1989, and first published in North America in 2005.
PLOT:
Art is a struggling dancer in New York who gets in a car accident. He's saved by a mysterious and beautiful young man with amnesia, who is quickly dubbed "Jimmy." Art takes the boy in, and the two start to bond. Then strange things start to happen: Art exhibits telekinetic powers, strange fish-like beings start to appear, and a boy from hundreds of years in the past comes looking for Jimmy. His past turns out to be tied to a a species of intergalactic merfolk, witch hunts, and the story of The Little Mermaid, and the more he remembers the more his life is in danger.
