Yuuki Kasumi

She is intelligent, competitive, and confident.
She is the epitome of a genius.
She is a Celtic witch from England that always carries with her a minion-type grimoire called "Nancy," modeled after a black cat familiar.

She is the head of the Yuuki family, one of the pillars of the Itsukino family, including Naoya, but due to past grudges, she tends to be harsh towards the twin siblings.