Kaze no Keishousha

Main character has an ability to see things not noticed by anyone like ghosts and monsters. Eventually he starts to work as a detective to be able to use his abilities for the benefit of other people. One day he meets a girl-like spirit who has no memory of her past. He can't send her to police since she's not a human. The two start to live together. At the same time, more and more spirits start to appear and trigger various incidents. What's the purpose of it all?