Of Darkness and Ruination by Rachel Fallon

Starlight in her veins, and a soul that calls for darkness.
On the magical continent of Celesterra, all humans are enslaved to the ruling fae…

Asteria Zagreus, a mortal young woman enslaved on Celesterra, must face Placement Day, the one day where all humans, at the age of Twenty-One, are placed in new kingdoms and given new masters to serve. Come Placement Day, Asteria is forced into the Dusk Kingdom and given to its Prince, Cyrus Tynan. When she refuses him and his desires, Asteria realizes she has only one option: escaping her enslavement and finding something thought impossible—freedom. Asteria must begin to play her own game within the court…and with the Prince of Dusk Kingdom himself.
Enemies come from all sides, however, and the merciless ruler of the Night Kingdom, King Calix Atarah Erebus, starts making his move against the Dusk Kingdom. Yet, darkness calls to Asteria in mysterious ways, and an equally mysterious soldier makes her question who the real monsters are—especially when it comes to a brutal king and a callous prince. With a bloody war brewing on the horizon, Asteria must decide who the true villain of her story is. Her choice, and the consequences of it, will ripple out across the continent.

Chaos rises, resistance gathers, and a soulmate bond is tested, while Asteria begins down a path that will change the course of history…