Dvasios ratas

Fuuta Okeya is a normal 14-year-old boy, except for the fact that he has the ability to see ghosts. A cute girl transfers into his class one day, but acts particularly aggressive towards him. This girl called Kouko Ishigami is followed around by a ghost called East. Fuuta tries to get along with her but ends up failing after she sees the birthmark he usually keeps covered. She then declares him as her enemy, his birthmark as a cursed brand and claims they have a long history, while talking about reincarnation. Who is this girl and how are they connected?