Fallin' for a Fallen. Holler & Hellfire, #1

Raelee "Dixie Deadshot" Calhoun plays converted feed stores up and down the two-lanes of eastern Kentucky, sleeps in her own truck, coils her own cables, and trusts no promise she can't carry out the door herself - a lesson hard-won from people who leave and a label man who went quiet. She is also the sixth generation of a Pike County matriline of mortal practitioners, an inheritance she keeps at arm's length until the night Route 119 puts a man in her path who is not a man.
Azazel is a Watcher. He came down through the Corridor on a mission of mercy and the passage tore the wings off him and knocked his very frequency out of true - the fall not as damnation but as static, a soul severed from the signal that made it whole. What he needs to come back to himself is the one thing Dixie has spent her whole life refusing to give anyone: belief, freely chosen, that can't be withdrawn.
What grows between them draws the attention of Heaven's enforcement. An assessor named Saraqael is dispatched to weigh the bond and end it - and instead, against every protocol, files no grounds, recommend closure. His mercy is a ceiling, and ceilings can be removed. By the time the sword arrives at the gate, Dixie has had to decide whether the rightness she's only ever found inside a song for two or three minutes a month is worth staking her life on for good - and whether a relationship built on trust and belief is, in fact, stronger than the oldest corruption in creation.
It is. That answer is the foundation the entire universe is built on.