Nozomi Kasuga is a classmate of Ouri, nicknamed Omune-sama or "Breast Goddess."

In the first chapter of the manga, she and a few other students visited a "man-eating house," where she was attacked and injured by a group of corpses. She was saved by Makina, and since then, she's developed a fascination with death. This fascination leads her to stalk Makina and later Ouri. She also becomes attracted to Ouri and desires to become a Shikabane Hime, so she can be with him forever.

In the anime, she was manipulated by Toya because they both thought death was beautiful. Toya's power transforms Kasuga, causing her to become more direct and eventually lead her to kill people at her school, until Ouri and Makina stopped her and Toya. However, they were unable to save Kasuga's life. With her last breath, she asked Ouri to make her into a Shikabane Hime. Her last wish goes unfulfilled as she didn't meet the requirements.

(Source: Wikipedia, edited)