Pai Ayanokoji, also known as Parvati IV, stands as the final survivor of the immortal Sanjiyan Unkara, a three-eyed demon race. Found in Tibet by Yakumo Fujii's father, her immense lifespan forged a split personality as a coping mechanism. Her primary persona, Pai, presents as a cheerful and naive human girl. Her secondary persona, Sanjiyan, emerges when her third eye opens, revealing a rigid, stoic demeanor and the ability to wield potent magic, though its use drains her severely. These distinct personalities coexist and communicate internally.

Though centuries old, she is considered young for her kind. Believing herself the last Sanjiyan and seeking escape from a traumatic past, Pai pursues the Ningen no Zō (Statue of Humanity), an artifact rumored to transfer Sanjiyan powers and grant mortality. Her destiny intertwines with Yakumo Fujii after she inadvertently transforms him into her immortal Wu protector following his death; this bond chains his existence to hers, meaning only her transformation into a human can restore his humanity.

Four years later, in *Seima Densetsu*, Pai resurfaces with amnesia, living as a high school girl named "Pa-bo." She remembers neither her true identity, Yakumo, nor her past. This condition stems from Benares, a follower of the demon god Kaiyanwang, sealing her memories using the demon snake entity Huàshé (Hawasho). Huàshé manifested three diamond symbols on her forehead and suppressed Pai and Sanjiyan, replacing them. As Pa-bo, she exhibits heightened emotional vulnerability, frequent distress, and dependence on Yakumo.

During the climax, Huàshé—having developed its own consciousness and identity within Pai's body—faces a critical choice: maintain the deception for Benares or shatter the seal to restore Pai and Sanjiyan, sacrificing itself. Huàshé chooses sacrifice, reciting a spell that destroys Benares and Kaiyanwang's altar. Following this act, Sanjiyan reemerges in control of Pai's body, though Pai's core personality remains dormant. Sanjiyan retreats to the Sanjiyan holy land to recuperate, instructing Yakumo to await Pai's eventual awakening. Huàshé is granted a separate physical form resembling Pai Ayanokoji but with brown hair and perpetually covered eyes, devoid of memories concerning Yakumo or their journey.

Pai's abilities include absorbing human souls to create nearly invulnerable Wu servants and accessing formidable mystical powers through her Sanjiyan persona. Her journey explores identity, sacrifice, and the coexistence of disparate selves, further complicated by Huàshé's emergence and dissolution.