Pai stands as the final survivor of the Sanjiyan Unkara, a race of three-eyed immortals. Discovered in Tibet by archaeologist Professor Fujii during his research into her people's legends, she journeyed to Tokyo seeking his son Yakumo's aid after the professor's death. Her objective: locate the Ningen no Zō, an artifact said to grant a Sanjiyan mortality. The weight of immortality fractured her psyche, resulting in dissociative identity disorder manifesting as two distinct personas. The cheerful, naive human-like identity Pai contrasts sharply with the rigid, magically capable Parvati, who surfaces during peril or emotional turmoil. The transition between these identities is signaled by the opening of her normally concealed third eye.

Her core narrative arc across all media revolves around becoming human to escape immortality's burdens and thwart the demon god Kaiyanwang from absorbing her powers. Yakumo's accidental death, caused by her pet Takuhi, led her to absorb his soul, transforming him into an immortal Wu bound to her existence. This act irrevocably links their fates: Yakumo can regain mortality only if she becomes human, while his death would follow hers.

In "Seima Densetsu," set four years later, Pai suffers amnesia and lives with an elderly couple, oblivious to her Sanjiyan heritage or connection to Yakumo. Her Pai personality dominates, reacting with fear and confusion when Yakumo finds her. Their quest to Tibet's Holy Land to restore her memories unveils suppressed aspects of her past, including an arranged marriage to Kaiyanwang (then known as Shiva) and encounters with followers trying to resurrect him. During this journey, her Parvati persona re-emerges intermittently as her powers reactivate during confrontations with adversaries like Benares.

Pai's character evolves from initial naivete and dependency toward heightened self-awareness and protective instincts. Her Parvati persona gradually softens, displaying genuine care for Yakumo and others, contrasting her earlier detachment. This growth culminates in her strategic decision to temporarily align with Kaiyanwang during the final battle. Exploiting his weakened state, she absorbs the souls of sacrificed Sanjiyan ancestors. This fusion grants her immense power to resurrect Yakumo and defeat Kaiyanwang, though she retains her immortality afterward.

Her abilities encompass energy projection from her third eye, soul absorption to create Wu, and transformation into animals for reconnaissance. However, utilizing her powers causes severe exhaustion, necessitating prolonged recovery. Later narratives depict her adapting to human society, adopting the surname Fujii, and serving as a supportive figure to her allies' families.