King of Coins by Amy Kuivalainen

Arkon, the Grand Sorcerer of Venice, grapples with two unyielding foes: duty and the enigmatic Wolf Mage. Unfortunately, he can’t escape either while the war with the Varangians continues to tear Europe apart.
Zarya Verasha, once loyal to the Emperor until his betrayal, seeks vengeance. Armed with a list of six names, she wants Arkon’s aid to take them down and end the war’s ceaseless turmoil.

The Varangians have created formidable war mages from the essence of magical captives, and it will take the combined might of Arkon and Zarya to stop them. As Fate weaves them closer together, Arkon and Zarya will discover unexpected similarities, forcing them both to question their perceptions of each other and themselves.