In the anime Mermaid Forest, the character referred to as mother is a central figure in the story arc known as Mermaid’s Mask or The Last Face. Her true identity is that of a grandmother who, twenty-five years before the events of the story, consumed mermaid flesh and became immortal. She attempted to take her grandson Nanao away from his father by convincing both of them to eat mermaid flesh. While Nanao continued to age normally and eventually fathered a child, she remained perpetually young. To hide the disfigurement caused by the mermaid flesh, she surgically grafted the face of a young woman onto herself, wearing it like a mask to dull her physical and emotional pain. Seventeen years after her initial attempt, she kidnapped Nanao’s two‑year‑old son and raised him for eight years under the false belief that he was her own child, even giving him the same name, Nanao.

Her personality is defined by a desperate, obsessive need for eternal companionship. She is manipulative and cunning, using lies and maternal affection to control those around her. Her motivation stems from the profound loneliness of immortality and a desire to recreate a family that will never leave her. She sees the consumption of mermaid flesh as the only way to bind her loved ones to her forever, and she will go to any length—including deception, kidnapping, and murder—to achieve that goal. In the story, she serves as an antagonist to the protagonists Yuta and Mana, who uncover her true nature and try to save the young Nanao from her schemes.

Her key relationships are with the two Nanaos: the first, her biological grandson who rejected her and escaped her grasp, and the second, the child she raised as her own son. She also interacts with the local doctor, Shiina, who becomes aware of her secret. The character undergoes no redemption; her obsession remains unbroken, and she continues to cling to her fabricated family even when exposed. Her notable abilities include immortality and rapid regeneration granted by mermaid flesh, as well as the surgical skill required to transplant another person’s face onto her own, allowing her to maintain a youthful appearance. She also possesses extensive knowledge of mermaid flesh’s properties, using its ashes to build immunity in others before attempting to feed it to them.