Fated to Monsters by Luna Pierce

Sometimes, the worst monster is the one that stares back at you in the mirror.
I was used as a pawn in a sinister war.
I spent my entire life slaughtering demons and consuming their souls one by one—now, I’m fated to three of them.
The secrets of my past haunt me, and the truth of who I really am comes as a shock to us all.
The only way to right my wrongs is to make sure it never happens again.
I must put a stop to the bloodshed and align with the very monsters whose lives I’ve threatened.
We will win this war if it’s the last thing I do.
One thing is certain: I can only save my people if I sacrifice myself.