Pai Ayanokoji is the last Sanjiyan Unkara, a three-eyed demon race possessing immortality. Her long lifespan forged dual personalities: the cheerful, naive Pai persona appears human with her third eye closed, while the rigid, magically powerful Parvati IV emerges when her third eye opens, usually during peril or distress. Both personae remain mutually aware and communicate internally. At roughly 300 years old, she represents a younger Sanjiyan with this split, contrasting older, often malevolent members of her race. Parvati wields devastating magic, though excessive use causes exhaustion requiring prolonged, vulnerable recovery. She retains memories of an arranged marriage to the Sanjiyan demon god Kaiyanwang before his descent into evil, the exact reasons for his corruption unclear. Centuries prior to the main events, she sealed Kaiyanwang after he slaughtered their race, an act later revealed to contradict her perceived vulnerability then.

Her core motivation is to become human using the Ningen no Zō (Statue of Humanity), an artifact believed capable of transferring Sanjiyan powers to grant mortality. This quest leads her to Tokyo seeking help from Professor Fujii’s son, Yakumo, following the professor’s death in Tibet. During their first meeting, her accidentally released pet demon Takuhi, freed by a thief, fatally wounds Yakumo. To save him, she absorbs his soul using her Sanjiyan powers, transforming him into her immortal Wu—a near-invulnerable undead servant. This irrevocably links their existences: Yakumo’s survival depends on hers, and he can only regain humanity if she becomes human. Their subsequent travels involve confronting demons and Kaiyanwang's followers seeking her power or the Ningen no Zō. Despite her often childlike Pai persona, she demonstrates moments of profound courage, occasionally shielding Yakumo. Her Parvati personality gradually evolves from aloofness to genuine care, influenced by her deepening bond with Yakumo.

A significant shift occurs four years later. She resurfaces with complete amnesia, living as a human high school girl named "Pai Ayanokoji" or "Pa-bo," devoid of memories regarding her Sanjiyan nature, Yakumo, or her past. This amnesiac persona is markedly different from her original Pai personality—more passive, prone to distress, and reliant on Yakumo for protection. Yakumo locates her, and they embark on a journey to recover her memories. It is revealed this amnesiac identity is not Pai, but a manifestation created by the snake demon Hawasho. Hawasho had been sealed onto Pai’s forehead as three diamond symbols by Benares (Kaiyanwang’s Wu) during a prior conflict, suppressing both Pai and Parvati’s memories and consciousness to prevent her power aiding Kaiyanwang’s resurrection. Believing herself to be Pai, Hawasho lived as "Pa-bo" under Benares’s influence. Faced with choosing to obey Benares or free the true Sanjiyan, Hawasho sacrifices her existence by reciting a spell. This destroys Benares and Kaiyanwang’s altar, breaking the seal. The true Sanjiyan personality (Parvati) reawakens in Pai’s body, while Pai’s consciousness remains dormant, requiring rest within their holy land. Sanjiyan displays uncharacteristic kindness, granting Hawasho a separate human life as a brown-haired girl named Pai Ayanokoji, who retains no memories of the adventures with Yakumo. Sanjiyan instructs Yakumo to await Pai’s eventual awakening in Tokyo, leaving the original quest for humanity unresolved. The Statue of Humanity’s whereabouts and secrets, last known with allies Ling Ling and Mei Shin, are not addressed during this arc.