カヤ

She is the sword-wielding oni who stole the sealed《Sword》from the Suten Group of the Onikiribe (Demon Extermination Organization), and is currently headed to a place where she has a strong karmic bond.
Solelo website

In fact, she is Shouko's mother's cousin, Kaya Narumi, who Shouko respects a lot. She was killed while trying to save her and resurrected as oni