Nagisa Akatsuki

Nagisa is Kojou's little sister who attends the same school as Yukina and is in the same class 3-C. She is also a close friend of Yuuma Tokoyogi and is good friends with Yukina Himeragi and Kanon Kanase. Her mother is Mimori Akatsuki. She is usually chatty with people she likes and is a very good cook. Four years ago, she almost died in a train accident which was caused by demons, she was and still is traumatized whenever she sees a demon. She was actually traumatized after being possessed by "Root." She first met Yuuma Tokoyogi after both Kojou Akatsuki and Yuuma retrieved her hat which was stuck on a branch at the end of a cliff. After they were safe everyone introduced themselves. (Source: Strike the Blood Wiki)