Halayda - Star-Fae Duology, #1

A mortal alchemist. A faerie king. A bond that transcends death. Betrayed by a trusted mentor, Sylvie Imanthiya hides on the fringes of society, caring for half-fae orphans and selling her alchemical creations on the black market. She lives for the one night each season when she can see her dearest friend-a man whose destiny is far above hers. King Taylan Ashkalabek knows better than to give his heart to a mortal.
Even their friendship is a risk; love is an impossible dream. Then a brutal alchemical attack poisons his realm, unearthing a dark power within him-and leaving Sylvie with the ancient mark of Faerie's savior. Manifesting unpredictable abilities and aided by allies with their own secrets, Sylvie and Taylan journey into the wilds of Faerie to heal the damage and confront Casimir, an invincible star-fae determined to rewrite destiny itself.
But only their enemy knows Sylvie's true capabilities-and Taylan's weaknesses-and how to use them in his vicious schemes. Her fate is life. His fate is death. With Faerie in the balance, Sylvie and Taylan must stand together before reality as they know it is destroyed.