Miu, a human-like yōkai of the Amami Tribe—kin to the Ghost Tribe—stands among the last survivors of her lineage alongside her younger brother Kai after their mother’s death. Her striking azure hair, neck gills, and sinuous tentacles reflect her aquatic origins, with her name echoing the Japanese word for "ocean" (海, "umi").

Upon her mother’s passing, Miu inherits the Jigoku Key, a revered artifact she later uses to rescue Kitarō when his spirit energy depletes from overexerting his Finger Guns. By transferring the key’s power to revive him, she reveals her resolve to protect others, driven by the grief of losing her mother.

Her yōkai lineage grants her mastery over water-breathing, rapid healing, and the ability to mend objects such as Kitarō’s Chanchanko effortlessly. She communicates telepathically, resists electrical assaults—even Kitarō’s amplified Yōkai Power—and wields retractable claws alongside formidable strength in battle.

Kind-hearted and reverent toward Kitarō, Miu harbors subtle romantic feelings for him, mirroring narrative threads from *After GeGeGe no Kitarō*, where a tribal heir like Mary revives and later marries him. Though her canonical role remains confined to the 2007 anime episode "Landing! The Threat of Western Yōkai" (Episode 32), her thematic resonance with legacy and sacrifice aligns her with broader lore across adaptations.