Spirit Circle

Fuuta Okeya is a normal 14-year-old boy, except for his perpetually bandaged cheek and his ability to see ghosts. A cute girl called Kouko Ishigami transfers into his class one day. He admires her, but she is angry and aggressive towards him. In contrast, the ghost of a man called East that follows her around seems happy to see Fuuta, although they've never met before.
Fuuta almost succeeds in getting along with her, but ends up failing after she sees the birthmark on his face that he usually keeps covered. She then declares that he is her enemy, that his birthmark is a cursed brand she gave him in a past life, and that they have a long history through many reincarnated selves.
Who is this girl and her ghost, and why does she think she must destroy Fuuta's very soul?