Ningyo no Kizu
English name: Mermaid's Scar
Genres: Drama, Fantasy, Horror, Mystery
Type: OVA, Episodes: 1
Aired: Sep 24, 1993
Studio: Madhouse
Source: Manga
Rating: R - 17+ (violence & profanity)
Synopsis:
Legend has it that when you eat the flesh of a mermaid, you would live forever. Yuta and Mana are living proof of this... Together, they journey to various places trying to find meaning for their existence, or perhaps even a "cure" for their situation. One day, Yuta and Mana meet Masato, a little boy who seems terrified of his mother Misa. It seems to Yuta and Mana that mother and son have a very unusual relationship. What happens when Yuta and Mana decide to discover the dark secret Masato and Misa are hiding? And what about those monster-like creatures that have been appearing?

(Source: AniDB)