The Fated and The Fallen (Fates of Aetherium#1) by M.E. Allquist:
 
He was bred to destroy her kind. She’s destined to destroy the world. But the Fates have a sense of humor…

A KINGDOM ON THE EDGE.
A POWER SHE CAN’T CONTROL.
AN ENEMY SHE CAN’T IGNORE.

The fragile peace between the triplet Kingdoms of Aetherium is fracturing. The anti-magic Border around Aeos is failing—and something dark is rising.

Hazel Callahan only wanted a quiet life alongside her father at their inn. But when forbidden magic bursts from her veins, she becomes a fugitive in a realm that hunts her kind. Her only hope for survival—and the truth about her mother’s past—lies with the one man sworn to destroy her.

Slaide Elias, the infamous shadow-wielding witch hunter, has spent his life serving the crown he despises. Hazel should be his enemy. Instead, she becomes his only chance at freedom—and the first to challenge the darkness within him.

Condemned to the deadly Tournament of Champions, Hazel and Slaide are forced into an uneasy alliance that ignites something far more perilous than magic. But as secrets unravel and destiny closes in, Hazel will have to decide if trusting her enemy will save her… or doom them both.

THE FATED AND THE FALLEN is the first installment in the Fates of Aetherium, an epic romantasy series featuring a high-stakes, slow burn, character-driven plot perfect for fans of Serpent & Dove, Spark of the Everflame, Serpent and the Wings of Night, and Throne of Glass.