I don't own Supernatural or any of the characters.
"Jimmy."
Under normal circumstances, that low, gravelly voice would seem welcome in this odd darkness. Contact was rare, and even if Jimmy didn't get along with the angel that used his body for a vessel, a conversation with him meant a break from being strapped to a comet. It meant, even if it was for a moment, he could relax. That's why, at the sound of his name, Jimmy looked up and smiled. Immediately, however, that smile faded.
Through the years, he'd grown use to his reflection staring back at him. Blue eyes, some wrinkles, and a slight five o'clock shadow. The expressions were never the same though, and often made Jimmy crack a smile on the best of circumstances, but from that solemn expression – that furrowed brow and escaping eyes – he knew this was not going to be a happy conversation. That's when he noticed the white gown in place of the normal suit and trench coat he wore. Was Castiel in the hospital again? Surely an angel wouldn't wear a medical gown without reason. Jimmy stood from his invisible chair, approaching the angel with a bit of caution.
"Castiel, what-"
"I... owe you an apology." Jimmy stilled and waited in silence for Castiel to elaborate on that. He never did.
"For what?"
"For me."
Jimmy jerked towards that new voice, a startled yelp escaping his mouth. An unfamiliar figure peeked through the darkness. Dirty blond hair stood out enough to frame piercing blue eyes, which were only drawn out by the eerie smile creeping on that slightly tanned face. Jimmy couldn't help the step back. Someone else was in his mind now. Someone he didn't know. "Castiel," he said, an uncertainty shaking his words, "Who is that?"
"Oh, we haven't been properly introduced, have we?" the man asked, tilting his head slightly. "I'm Lucifer." The man stepped towards him, hand extended. Lucifer? The devil? Jimmy took another step back, his eyes widening as his breath caught in his throat. Then Castiel stepped in the way. Lucifer's face softened, that smile fading into a pout as his hand fell to his side.
"Stay away from him." If this was Castiel's attempt at being assertive, it lacked. His voice was too soft. The low roar rolling in his gravelly voice did help, but not enough. Lucifer cocked his head, that pout still lingering.
"I'm only trying to be nice," he cooed, those eyes moving from Castiel to Jimmy, "After all, we'll be sharing this mind for a very, very long time."