Thirteen-year-old Tokyo resident Mana Inuyama contacts the yokai Kitaro seeking help for her neighbor Yuta, who witnessed people transforming into vampire trees. This draws her into the supernatural world, revealing the existence of yokai and forging an alliance with Kitaro despite his initial reluctance to involve humans in yokai affairs.

Mana lives with her parents, Junko and Yuichi Inuyama. She has an uncle, Shoji, and an aunt, Rie, in Sakaiminato, and a great-aunt, Toshiko Sawada. She maintains close family ties, frequently visiting her relatives during summer vacations. Mana has brown hair styled in a short ponytail on her left side, fair skin, and blue eyes. She typically wears a white hairpin with a pink circle above her left ear, and her clothing ranges from casual cat-themed outfits to her school uniform.

Mana embodies a highly curious, cheerful, and brave personality. She displays strong protective instincts, especially against bullying, and believes older siblings are responsible for their younger siblings' behavior. After encountering yokai, she develops a deep fascination with them and actively seeks to understand their world. Her courage allows her to take significant risks to assist both humans and yokai in dangerous situations.

Her relationship with Kitaro evolves from mutual skepticism to firm friendship. She repeatedly demonstrates loyalty by assisting him against malevolent yokai, despite his early warnings about human-yokai dangers. Mana forms a strong bond with Neko-Musume, admiring her and affectionately calling her "Neko-neesan." This bond suffers severe strain when Mana witnesses Neko-Musume apparently attacking her mother, leading to a tragic confrontation where Mana accidentally kills Neko-Musume using newly manifested defensive powers, causing significant emotional trauma. She also befriends the witch Agnes, receiving protective magic through a "Witch's Kiss" granting immunity to certain supernatural effects and access to the GeGeGe Forest.

Through her experiences, Mana gains spiritual awareness, allowing her to perceive yokai invisible to most humans. She later becomes an involuntary spiritual vessel for Nanashi, the resentful spirit of her ancestor Fuku's unborn child, who infuses her with malice. This connection grants her defensive powers manifesting under extreme duress, including a spiritual blast capable of annihilating yokai. She eventually gains voluntary control over these abilities. Five elemental seals placed on her by Nanashi correspond to Wu Xing philosophy: Wood, Fire, Earth, Metal, Water.

Key story arcs shape her development. Early episodes establish her role helping Kitaro combat threats like the Nobiagari and rescue children from Tantanbo's yokai castle. Her connection to Nanashi forms a major storyline, revealing her lineage to Fuku and culminating in her helping Nanashi find peace by giving it a name and showing compassion. The accidental killing of Neko-Musume represents a profound emotional breaking point, followed by Neko-Musume's temporary regression to a childlike state. Mana confronts the human yokai-hunter Rei Isurugi, challenging his hatred while learning about Kitaro's deal with Enma-Daiō. In the series finale, she sacrifices all memories of her yokai friends to resurrect Kitaro, eventually regaining partial recollection years later.

Her background connects to deeper lore through her ancestor Fuku, whose tragic death created Nanashi. This ancestral tie explains her selection as Nanashi's vessel. The unknown "Power of Luck" mentioned in her profile occasionally manifests through improbable but fortuitous occurrences during battles.