Crystal Crowned (Air Awakens #5) by Elise Kova

Long live Solaris.

One bloodthirsty ruler has been overthrown by another, casting the shadow of death over the Solaris Empire. Vhalla Yarl stands upon the stage of fate, prepared to do battle one final time. Fragile alliances will be tested and new bonds will be formed as the world is reshaped. She fights as the champion of peace, but when the night is darkest will she be able to pay the price of a new dawn?