Sunsplitter by S.A. MacLean

Fi has toppled immortal beasts. Antal welcomes being conquered. After helping the Lord Daeyari reclaim his territory, semi-reformed smuggler Fi dons a daunting new role: rebuilding a city alongside her monstrous partner, a haven free from bloody sacrifice. So when Antal's father unexpectedly summons him home, Fi's first instinct is to ready her claws. Only, claws won't be enough for this adversary. Antal faces his first homecoming in five decades, dreading two truths. From his father's seat on the governing council, he could undo everything Antal has built. And their last argument ended with Antal's lover dead on the floor. But a greater danger lurks: the appearance of a creature that even the daeyari fear, burning its way through the Planes. With Antal's father leading the hunt, he and Fi must ally with a team of immortals who could turn fangs on them at any moment. Or worse, strain their still-fresh love until it snaps.