Mao

The creature known as Byoki began its life as a simple house cat in the late Heian period. Back then, it was called Haimaru and belonged to Sana, the daughter of a powerful onmyodo master. Shy and timid, Haimaru shied away from anyone except its owner, who carried it almost everywhere. The only other person it seemed to tolerate even slightly was Mao, who managed to pet it when no one else could.

Finally, Haimaru was kidnapped by Mokuzu, a naive gardener to whom he promised great power if he helped him with a nefarious plan to sabotage the school. Mokuzu stole the cat and threw him into a pit filled with poisonous creatures and wild animals. Surprisingly, the cat was the only survivor, but he changed radically after devouring the poisons and blood of his vanquished enemies. He evolved into the powerful feline demon Byoki. Freeing himself from his bonds, Byoki devoured the sacred texts of the Onmyodo temple, acquiring knowledge to later attack its practitioners. Originally intended as a weapon against other schools, Byoki turned against his own teachers and murdered indiscriminately.

Otoya, Mao's loyal assistant, appears to be a child with a calm and mature personality beyond his years. He shows no signs of mischief or other childish behavior, for he is not actually a child; he is a shikigami, a type of familiar spirit whose soul is infused into an object. In Otoya's case, his spirit was deposited into a small wooden doll that resembles his childlike appearance. He always calls Nanoka "Nanoka-san," just as he calls Mao-sama.

Mao, a young mystic living in Taisho-era Japan at the beginning of the 20th century, is a mysterious onmyoji who, after suffering a life-changing curse, has lived for nine hundred long years.