Ecliptic by Kristin Travis

Keira made a deal with the Dark Spirit Erovos—her life in exchange for the safety of the people she loves. She thought surrendering herself to the enemy would mean the end of the battle. Instead, it’s the start of war.
As Erovos prepares for conquest, Keira races to find allies in a fracturing and dying world. Yet, to rise as a beacon of Light, she must first reckon with the demons of her past, but the darkness is closing in, both physically and mentally. And as Keira’s mind and power slip, she fears she will become the very weapon Erovos needs to bring about the destruction of worlds.
Entangled in a web of failed prophecies, politics, and passion, Keira and Rowen’s love is put to the test, and a mysterious interloper threatens the core of her beliefs. As war looms ever closer, Keira is forced to choose between the flame that anchors her and the fate of everything she holds dear.
Will a failed prophecy doom Luneth forever? Or will Keira eclipse the encroaching darkness, saving her new home, her Light, and her love?

Ecliptic is the seductive and spell-binding conclusion to Synodic.