The Blood that Binds Us by Erin Mainord

She is the wielder of blood magic,
and she may end them all.

“Monster…”

Wren has never stolen a life, but that doesn’t stop her from believing her darkness makes her a walking nightmare. Harboring a power so lethal, unpredictable, and entirely forbidden by kingdom law, Wren’s spent her whole life hiding what she is—who she is. A bloodwitch.
Meanwhile, a war is looming, and Wren’s feral magic may be the only thing that can stop the uprising from destroying the kingdom, her home, and everyone that stands in their way. After her sister is captured by the rebellion, Wren must seek help from the kingdom’s ruler who would sooner imprison her than offer aid. Except… Singard needs her, and when she volunteers the use of her power in exchange for his help finding her sister, an unlikely alliance is born.
Forced into a reluctant compromise with the “white-haired witch,” Sin finds himself protecting Wren for his kingdom’s survival, but their star-crossed relationship quickly spirals into one straddling the precipice of hate and passion. As secrets are unveiled and loyalties are tested, neither are sure who they can trust.

When hostilities deepen and war draws near, Wren is determined to rein in her wild magic and bind it to her will. With the lives of everyone she loves at stake, Wren must look within and decide if she is the monster she fears, or if there is light to be found in the darkest parts of herself.