A kingdom of ruin by K.F. Breene

Never sell your soul to the Demon King.

Too late.

In an effort to save all that I love, I have to finish the job Nyfain started… and ruin myself.

I've made a trade with the most cunning creature alive.

Me for them.

The dungeons will be my new home. Dolion's destruction will be my new goal.

I just have to get out of here and back to my golden dragon. Preferably alive.
 
- Goodreads Summary