Just a drabble that exists in a non-canon vacuum where Dean and Cas are exploring their profound bond and Balthazar is Not Happy about it.
"So," Balthazar, as usual, appeared out of nowhere, his only herald the snap and crackle of the street light behind Dean. "You and Castiel, hm?"
Never happy to see this particular angel, Dean scowled, adjusting the bags in his hands defensively. That he was carrying too many hamburgers for himself and Sam was fairly obvious. "He's crashing with us tonight. You got a problem?"
"Maybe." The blue eyes were cold. Bitter.
Dean's lips twitched. "Jealous much?"
Balthazar pressed in closer, invading his personal space. He smelled like brandy, ozone, and expensive cologne. "That's none of your business, boy. I want to know what your intentions are toward my brother."
The idea of dissipated, sarcastic Balthazar showing familial protectiveness was so foreign, the hunter actually laughed. "Wait, what?"
"You don't have a good track record." Was that a smirk? If so, it was completely without positive emotion. "I hear you fucked my sister and later on just stood by and let her be killed."
Ouch. Dean swallowed, gaze flicking around for just long enough to confirm there was some lingering bad feeling, but rallied quickly. "Well, if she hadn't tried to kill my parents…"
"I'm running out of siblings. I intend to hold onto the one I have left. Don't damage him." Threat dripped from the words.
Dean stepped back, frowning, and turned to go. He'd never quite gotten Balthazar. Too slick, too dishonest, too smug. This, though, he understood. "Duly noted," he said, admitting nothing but acknowledging the other angel's bond and claim in his own way. "I'll tell Cas you said hi."
"Hm. I'll be watching." The soft rustle of wings told him the other angel had gone.
He was almost at the door to their motel room before the streetlight came back on.
