Three sentence fic (source)
When Arthur saw the hairline fractures along Lewis’s locket, when he saw the veins of pink light bleeding out between the fingers of the man in robes, he didn’t hesitate.
Lewis had never seen rage so etched into Arthur’s face, but he had the fullest view of it now, where he was on the floor beside the necromancer holding his anchor. Arthur’s lips were curled back as far as they could go, pink light reflecting off razor teeth. He had taken to the air- something Arthur never did, and his wings were spread wide until they blotted out everything else in alternating beats, shrouding them in just the afterglow of his heart before buffeting them with furious gusts. The only other light was Arthur’s eyes, pupils pinpricks and the irises aglow in golden fire. Even blunted, his claws looked sharp as blades, and with a harsh flap, his wings came up, and his talons came down.
The man cried out as he fell beneath clawed feet with the sound of cloth tearing and something heavy hitting stone. His clothing was shredded in the landing, and shallow cuts where Arthur’s feet had nicked his skin turned to thin red lines. Arthur’s wings came down next, making him flinch as they slammed into the ground on either side of his head and cracked the flagstone. They were still spread, and it caged the two of them in complete black, except for the blazing embers of Arthur’s eyes.
Arthur’s hands came down. He grabbed the front of the man’s robe and pulled him up by the collar, so their face was inches apart. He pulled him so close that his own visage was visible in the reflection of wide eyes. Eyes that moved between Arthur’s own and his fangs. Fear had drained the color from the man’s face and snatched the smug grin he’d had from his mouth, especially while he remained immobile, arms and chest pinned hard to the floor and a demon inches from his neck.
Arthur’s tail moved and snaked the heart from the necromancer’s shaking hand as he pulled him closer, claws just brushing his shoulders and bobbing throat. Arthur bared his teeth just a touch more, before hissing in his ear. “You will never. Touch. Lewis. Again.”