Yui is the daughter of human and a Shi (another type of demon, also described as anti-shinma in some English translations). She is also part vampire as Miyu's blood runs in her veins, as Miyu fed on her mother while pregnant with Yui. Miyu describes Yui as both her sister, her daughter, and herself. Yui has long dark hair, and looks to be about twelve or thirteen years old. Like Miyu, Yui has a tragic past and friends she had to abandon upon her awakening. Yui has the additional issue of being both hunted and supported by rival factions of Shi, who do not approve of her existence.