Emberheart. Soulfire Chronicles, #3

Their bond saved two kingdoms. Now it must save the world. Six months after brokering a fragile peace, Elara and Kael have transformed Sanctuary into a beacon of hope-a city where 2, 000 souls from both kingdoms live in harmony. Bonded pairs, war refugees, and those who dare to dream of something better. But Mordain, the zealot who once called Elara sister, has returned. His Pure Flame faction believes bonded pairs corrupt magic itself, and they're willing to kill to prove it.
When assassins strike in the night, murdering three bonded pairs in their sleep, the message is clear: peace is an illusion. For Elara, the stakes have never been higher. She's carrying the first known child of a bonded pair in centuries-a pregnancy that makes her both a symbol of unity and a target. Kael's protective instincts are driving them apart at the very moment they need each other most. Then the Dead Zone begins to fracture.
Ancient texts reveal the truth: the kingdoms weren't divided by war-they were split deliberately to prevent a prophecy. To stop the awakening of the Cinder King, an entity of pure destructive fire that nearly ended civilization two thousand years ago. Unified magic doesn't cause the awakening. It's the only thing that can stop it. When the Cinder King rises, both kingdoms must finally unite or face extinction.
But victory demands the ultimate sacrifice: Elara and Kael must bond with the entity itself, becoming eternal wardens who will carry this terrible power within them forever. Some love stories end with happily ever after. Others end with a choice: walk away, or stay and guard the door so others can live free. The Soulfire Chronicles concludes with its most powerful love letter yet-to sacrifice, hope, and the bonds that make us human.