Wings of Ash and Amber

She fell from Heaven for refusing a monstrous order. He was born on the wrong side of a line drawn through the world before he existed. Neither of them were looking for an alliance - but when an ancient force begins unmaking the foundations of the mortal realm from the inside, the Compact binds them together whether they want it or not. Lyari has spent four years building a life from what the fall left her.
She's good at it. She doesn't need a demon general reading her containment markings and telling her what she already knows. Aymer has spent three centuries being exactly what Hell required. He's very good at that too. He doesn't need a fallen angel who goes directly to the center of every problem and refuses to look away from things that are wrong. They're both lying. The threat they're facing is older than the separation of the realms, smarter than either of them anticipated, and working from a wound so deep it has started to look like a cause.
Stopping it will require everything they have - their power, their history, the careful things they've been building toward each other since the moment they met in a ruined city and decided, separately, that they were not going to be the first to admit what the other was worth. The banter is lethal. The chemistry is more dangerous than the apocalypse. And whatever comes out the other side of the fire they're walking into will not be what either of them was before.
Some transformations are worth the cost. Wings of Ash and Amber is a slow-burn enemies-to-lovers fantasy romance featuring a fallen angel FMC, a demon general MMC, forced alliance, forbidden species, world-at-stake stakes, and a love story that builds from hostile competence to something neither of them has language for until they find it in a tongue old enough to hold it.