Legend states that eating the flesh of a mermaid will bestow immortality. Yuta and Mana do not remain dead for this reason. Unfortunately, mermaid's flesh affects people differently. Trying to help her sister Towa, Sawa creates a problem that will affect both of them for the rest of their lives. And now Towa's plans threaten both Yuta and Mana.
(Summary Courtesy of Anime News Network)
Single OAV episode released on August 16, 1991.
Animated by Studio Pierrot and TMS Entertainment
Based on the story from Rumiko Takahashi's Mermaid Saga manga series.
Formerly licensed by Central Park Media in the 1990s where it had a VHS release before CPM's rights to it expired.
Also see the later chapter of Mermaid Saga in OAV form, Ningyo no Kizu
and the 2003 TV anime remake of Mermaid Saga stories, Ningyo no Mori