Mana is Yuta's traveling companion. By immortal standards she is young, probably in her 30s, but she was fed the flesh of a mermaid when she was 15. Mana was held captive at Cape Nosuri by mermaids who raised her. She was kept indoors most of her life, and her feet were bound so she was never able to walk. A mermaid named Ayu was sacrificed and fed to her. Mana survived eating the flesh, a truly rare feat and gained immortality.
The Meaning Behind the Name
Mana is made up of two kanji. The first being for "truth" and the second for "fish". Mana is also defined as "a dynamic supernatural power dwelling in and flowing from certain individuals, spirits, or things and capable of producing great good or evil".
Lalainia Lindbjerg, who plays Mana in the Mermaid Scar OVA has quite a few credits to her name including Natsume in Ranma ½, Hari in Inuyasha: Affections Touching Across Time, Bulma in Dragon Ball Z and Alice Sakaguchi in Please Save My Earth.
Karen Thomson plays Mana in the TV series, who's other roles include Shinobu Nagumo in Patlabor: The Movie and it's sequel, as well as Seri Takekami in Fafner, Sayaka Kanazaki in Boys Be... and Ritsuko Hirooka in Rumiko Takahashi Anthology.