Captive by Caitlin Ricci

For centuries, Sebastian de la Sang has been his father’s perfect heir: a vampire prince enhanced with brass machinery, drained of emotion, shaped into a weapon.

Then the orcs take him.

Bound beneath the Heart Tree, Sebastian expects death. Instead, he gets transformation. Ancient orc magic awakens something in his brass augmentations, stripping away his father’s control and leaving him dependent on his captor’s blood to survive.
Boarstaff should kill him. Instead, the orc warchief feeds him.
As Sebastian changes, Boarstaff begins to see not an enemy, but possibility. And when Sebastian offers intelligence to save a human child from the vampire citadel, their fragile connection faces its first test.
Attraction builds between captor and captive. The rescue will succeed. But the price will be higher than either imagined, and the war coming for them both has already begun.

Captive is a dark MM fantasy romance featuring enemies to lovers, slow burn attraction, intimate blood feeding, found family, and devastating consequences. First in the Brass and Bone trilogy.