18+ Zero: Circle of Flow

Gi Yuh is the leader of the strongest gang in his high school. He lives together with his younger sister, who seems to love him.
When saving the beautiful Ha Na from a truck he instead gets injured and lies in coma for two weeks. During these two weeks he dives into a strange dreamworld and after his recovery he is not the same anymore. He regularly dreams about what seems to be a past him. To find out what happened to him he asked his teacher for help, who has friends, who deal with fortunetelling and supernatural powers. Here he finds the answer to his strange condition: He is supposed to be a "higher" ghost", who takes the position of a dead or soon-dying person.

(Source: MU)