The Castle Floating on the Sea
The Little Prince befriends a boy who claims to have seen a mermaid and a floating castle, but no one believes him. Source: crunchyroll
Aired 15/08/1978EP 7 - The Castle Floating on the Sea
1978
The Adventures of the Little Prince
The Little Prince lives on Asteroid B612, a tiny rock floating in space. He spends his days cleaning out the three small volcanos on the asteroid (which he also uses to cook his breakfast), weeding out the baobob trees that threaten to take over, and caring for his friend the Rose Girl. When he gets lonely for company he catches a comet in his butterfly net and flies off to Earth for all sorts of adventures.
(Source: Anime News Network)