Eyes of Devious Burgundy: Deathcaller Duet, Book 1 (An Age of War and Prophecy)

Using magic was the same as using any muscle—it required work to build it and time to rest it. The flashes of white and black magic had died down until only a few remained standing, stained ruby from their fight and wielding whatever power they had left. If this cycle were doomed to repeat itself with a mate, then what was the point in living? That was, after all, how Banand and his magic had been discovered, and why the Angels sacrificed themselves in droves to get him.