Nix - Nix Trilogy, #1

Demonic possession...from the demon's point of view. Dark horror for the twisted mind. Nix has one goal: escape. Hunted by the demonic hierarchy for a murderous joyride that she may have committed but definitely wasn't responsible for, Nix has been jumping from one unwilling host to the next in order to stay hidden-and it was working, for a while. But Nix soon finds that there are other hunters closing in. Desperate, she borrows the body of a young paranormal hunter named Rachel.
All Nix needs to do is lead the hunters away, and then disappear. Hiding among the hunters seems brilliant at first, but of course nothing's ever that easy. Trapped inside the uncooperative hunter, Nix is damned if she leaves and damned if she stays. Even worse, Nix discovers that her idiot hunters are involved in a nasty plot to destroy the world-and sure, Nix loves chaos and destruction as much as the next demon, but she still has to live in that world.
Nix has objections to that sort of nonsense. Nix isn't the hero the world deserves, but she's the hero it's damn well going to get.   Note: This book contains graphic violence, gore, and sexual content. Reader discretion advised.