From the introduction:
Consecutive disappearances of men and women have become rampant in Karadate City, Hokkaido. Police seem unable to solve or stop these incidents and what clues they do have don’t seem to make sense: figures crawling out of bloodstains and sightings of huge animals at night. At least, that’s what they say. It seems Karadate City is the center of a rather grand occult conspiracy. In cases like these, the Police call upon the expertise of a beautiful Sweeper by the name of Nosogi Ren.
Sweepers, those who hunt monsters, are one of but many individuals who call the underworld of society home. Those that hide that the occult is actually more real than anyone could ever imagine. Exorcists, Magicians, Cults, all of these interact with the seedy underbelly that is the criminal underworld.