Sailor Ray and the Darkest Night (The Pact Book 1)

I suppose I choose this life, but often times I wonder if the choice was really my own. My name is Sailor Ray, and I'm a demon hunter. There are others like me but we all do what we do for our own reasons. Some want to make the world a better place, while others want balance. I just want revenge.
On the day my father died, I made a pact with a devil, Alfonse. In exchange for saving me from the same fate as my father, I promised him my body as a vessel, and once my revenge is obtained, my soul will also be claimed by him.
I was only using him, and he was already using me. Neither of us planned to keep our end of the deal. When our pact was first made, he was weak, a dying spirit. Now, as he heals within me, I can feel his presence growing stronger with every passing day. I'm not stupid, though.

He plans to take over, and I plan to kick him out.

There's a new lead on the demon who killed my father. First I kill him, then Alfonse.
Easier said than done.