Kasai is a character in the Given series and a classmate of Ritsuka.
Kasai has short Persian orange hair with similar-colored eyes and she wears a light brown cardigan like a school uniform with a white buttoned undershirt and a red string tied in a bow around the collar.
She is very honest and truthful about her feelings towards others, but get's jealous over other people's relationships, especially between Ritsuka and Mafuyu. She discussed matters openly with her friends and was the first to have some notion of Rituka's feelings concerning Mafuyu. Though at first willing to make some attempt to drive a wedge between them by bringing up Mafuyu's past, she felt bad about doing this and said as much to Ritsuka.
Kasai and her friend walk together through Shibuya only to spot Ritsuka and Mafuyu. Her friend happens to know something about Mafuyu and begs to tell her.