"Mermaid's Scar" is a dark fantasy anime OVA based on the manga by Rumiko Takahashi, set within the broader "Mermaid Saga" series. The story centers on Yuta, a man who gained immortality centuries ago after consuming mermaid flesh, and Mana, a young girl who shares a similar fate. The two travel together, seeking a way to end their eternal lives, as immortality comes with a heavy toll: the constant threat of madness and the curse of outliving everyone they care for.

The narrative unfolds when Yuta and Mana arrive in a coastal town, where they encounter a wealthy family embroiled in a sinister struggle over a mysterious artifact known as the Mermaid's Scar. The artifact is said to grant eternal life, and its power becomes the focal point of greed and desperation. The family's matriarch, a woman named Masato, is revealed to have used the scar to maintain her youth and vitality, but her immortality has come at the cost of her humanity. Her adopted son, Shingo, resents her for her cruelty and seeks to destroy the scar, believing it to be the source of his suffering.

As Yuta and Mana become entangled in the family's conflict, the story delves into themes of mortality, the corrupting nature of immortality, and the lengths people will go to escape death. The tension escalates when it is revealed that Masato has been sacrificing young girls to sustain her immortality, and Mana becomes a target. Yuta, driven by his protective instincts and his own experiences with the curse, intervenes to save Mana and confront Masato. The climax is marked by a violent confrontation that exposes the true cost of immortality and the fragility of human desires.

The characters are defined by their struggles with the consequences of immortality. Yuta is a weary traveler burdened by centuries of loss, while Mana represents innocence and the hope for a resolution to their shared curse. Masato embodies the darker side of eternal life, consumed by her obsession with youth and power, while Shingo serves as a tragic figure caught between hatred for his adoptive mother and his own desire for freedom.

The OVA is a self-contained story that explores the moral and emotional complexities of immortality, set against a backdrop of supernatural intrigue and human drama. Its concise narrative and focus on character-driven conflict make it a compelling entry in the "Mermaid Saga."