Kuze Kiriha

Kiriha is one of Kouhei's classmates. She is most often seen alone, and will not talk much, even when spoken to directly. She does not have many interests, and is in no clubs. She has been exceptional in math ever since she was young. She is a vampire servant, which makes her immortal and she has superhuman powers, though she does not need blood and has dulled senses of taste.

Edited from Wikipedia.