Yuuki Kasumi

The main heroine of this work.

A mysterious girl who suddenly appears in Naoya's time of need and saves him.
She always carries with her a grimoire modeled after a black cat familiar called "Nancy."

She is competitive and confident, and is the epitome of a genius.
However, she often makes devilish remarks to Naoya, causing him trouble.

Although she is wary of Fujinomiya Atsushi, She is accepted by Ichika and Saya and she ends up living with the Itsukino family.