Lullaby of the Sword by Niki Trento

A Demon
A Sword
A Destiny

Styx was abandoned Topside as a small demon. Left to fend for herself in the human world, she does the best she can. Working as a stripper at the French Tickler, she kills demons in her time off—when they aren’t being inconsiderate scourges. It’s a good thing her sword loves some demon blood.
Kyon was blessed by the great Aphrodite when he was a few years old. He didn’t know it then, but he was given the ability to find his fated mate. Something those of his kind never expected to have.
When a demon threatens all that is precious to Kyon, he teams up with Styx to protect the Underworld at all costs. Will they be able to solve the mysteries of deception and motives before it is too late?