She is a vampire and a friend in Nico Hirata's clique.

Spoiler

Before becoming a vampire, Kabura was a very sick, but kind person, who couldn't go out with her friends much, and stayed in the hospital with Haru Nanakusa, as anything her friends want her to do were too much energy for her. Later, she wanted a way out of the hatred and neglect from both family and friends, so she agreed on the request of being turned into a vampire by Haru.