Evermilion

Evermillion (エヴァーミリオン?), fully named White Princess Evermillion (白姫エヴァーミリオン Shirohime Evamirion?), is an entity of unknown origin sealed inside Honoka Takamiya. She is addressed as the White Princess by various characters. A total of five seals were placed on her.

(Source: Witchcraft Works Fandom)