This is a cool little gem. It reminds me a bit of Ushio & Tora, mainly because of Nue's true form. Judging from the later volume covers, it seems Rei will either be a constant target of the other side and Nue sticks around because of all the free food, and/or she accidentally gains some sort of power from the other side that binds Nue to her, a bit like Zenki and Chiaki. I do miss those types of manga.
The art style is simple and effective, but it can look awesome at times. The Volume 4 cover with Rei resting or whatever inside Nue goes especially hard.
Katayama is such a huge prick he had the nerve to argue about that pocket change Rei asked for right in front of the monster who just saved his life lol, I'd get a new job ASAP if I were her. Flipping burgers or manning a conbini cashier isn't as degrading as working under that dude.