A/N: This is a divergent ending of "Swan Song" (season 5, episode 22). Just a little something I needed to get out of my head. It's not my favorite, but oh well.
The song I listened to while writing this was Oats in the Water by Ben Howard. Might be worth listening to as you read, if you enjoy that.
So I used some dialog from the episode (which I do not own, by the way) as a refresher as to how it went down leading up to where my version diverges. It starts where they confront Lucifer with the intention of saying "Yes" and diverges when Lucifer takes over Sam. Up until that point, the dialog is practically copied and pasted from the episode. If you know the words like the back of your hand, feel free to skip it.
This does not have a happy ending. Enjoy.
"Sorry if it's a bit chilly. Most people think I burn hot. It's actually quite the opposite." Lucifer mentioned conversationally.
"Well, I'll alert the media." Dean snarked.
"Help me understand something guys. I mean, stomping through my front door is... a tad suicidal, don't you think?"
"We're not here to fight you." Sam asserted, no trace of fear behind his eyes.
"No? Then why are you?"
"I want to say 'yes'."
"Excuse me?"
The demons flanking Lucifer dropped.
"Chock-full of Ovaltine, are we?"
"You heard me. Yes."
"You're serious."
"Look, Judgement Day's a runaway train. We get it now. We just want off."
"Meaning?"
"Deal of the century. I give you a free ride, but when it's all over, I live, he lives, you bring out parents back -"
"Okay, can we please drop the telenovela? I know you have the rings, Sam."
"I have no idea what you're talking about."
"The Horsemen's rings? The magic keys to my Cage? Ring a bell? Come on, Sam. I've never lied to you. You could at least pay me the same respect. It's okay. I'm not mad. A wrestling match inside your noggin... I like the idea. Just you and me, one round, no tricks. You win, you jump in the hole. I win... well, then I win. What do you say, Sam? A fiddle of gold against your soul says I'm better than you." Lucifer taunted lightly.
Sam rolled his shoulders and took a composing breath. "So he knows. Doesn't change anything."
"Sam."
"We don't have any other choice."
"No."
"Yes."
A blinding light filled the room. When Dean was able to open his eyes, Sam was lying motionless on the floor. It took everything he had, but Dean ignored his urge to check over his brother and try to wake him up. Instead, he removed the rings from his pocket and glanced at them for only a moment before throwing them at the wall and muttering the incantation.
The torrents of wind that blew through the portal completely masked the wingbeats the disturbed the air in the corner of the room.
Sam stirred and Dean finally relented to his need to go to his brother. "Sammy!"
A deep mumbled incantation came from the corner of the room. Dean whirled on his heels to identify the source and eliminate it, but nothing was there. The next second, the whistling wind stopped and Dean whirled around to find the portal had closed.
With a groan, Sam hefted himself to his feet, but Dean could already see that Sam wasn't the one in control. His brother had lost.
Wingbeats stirred the air beside Dean, and a familiar coat flapped in Dean's peripheral. Dean didn't have the time or presence of mind to question why the recently humanized angel had his wings again; his mind was still stuttering over how completely they had failed. He had lost Sam for nothing.
"Dean." Cas's gravelly voice broke Dean out of his trance, his comforting hand on Dean's shoulder grounding him as he slowly hefted himself to his feet.
"Castiel." Lucifer greeted rather warmly, his excitement and joy at finally winning not allowing any dampener to affect it. Dean's disgust towards the devil grew as he gloated in the face his vessel's and his own brother.
"Lucifer." Shock colored Castiel's voice, nervousness making it almost vibrate.
Dean, however, was past his shock and ready to take action. "Cas, the rings!" Dean cried out as he full on body tackled Lucifer. It wouldn't have worked against his gigantor brother normally, but now that an Archangel possessed him, Dean didn't make him budge an inch. Dean was sent flying back and he crashed into the wall.
Cas was prying the rings from the wall when Dean's vision cleared. Lucifer had directed his attention to the angel and Cas had bravely turned to face the archangel, the rings held loosely in his hand.
"The rings, if you will, Castiel." Lucifer gestured towards the angel, extending his hand to receive the rings as if he just expected his brother to fork it over and thank him for the privilege.
The scaley voice that emanated from his brother's mouth made Dean bristle. He already had an insult to sling at the Devil on the tip of his tongue, hoping to distract him long enough for his angel to get away, when Cas stepped forward. Dean's head turned on stiff hinges as he watched his angel walk calmly towards Lucifer.
"Cas?" Dean questioned haltingly. His thoughts bounced all over the place as he tried to figure out exactly what his friend was doing. The conclusion he came up with was that Cas was sacrificing himself and the rings to allow Dean to escape. Dean didn't want to allow Cas to do something so idiotic, but he found himself unable to do anything more than say the name as he watched Castiel transfer their last hope into the Devil's waiting hands. Lucifer broke into a wide grin and Dean felt sick.
Lucifer lunged forward suddenly and Dean was sure that Cas was done for. His best friend was going to be evaporated while he watched helplessly in the corner.
But that isn't what happened. Sam's lanky arms enveloped Cas as Lucifer pulled his younger brother into a tight hug, his head hanging down on Castiel's shoulder as his own shook with laughter and joy. "Thank you, Castiel." Lucifer's voice was strong and emotional as he thanked his brother. Dean felt himself shattering.
The last straw was when Cas's lips curved up more than he had ever seen before, and Cas returned Lucifer's hug with the same veracity. "Welcome back, brother." Cas muttered.
Lucifer finally pulled away from Cas, but kept his hands on his shoulders and looked him in the eyes with sincerity. "I don't know what I would do without you, Cassy."
"Burn in Hell, most likely." Cas replied good-naturally.
Dean's heart stopped.
Both angels seemed to have forgotten Dean was in the room as they shared in the joy of a long awaited victory and Dean edged back in sheer terror at the implications behind it. Unable to watch for a second longer, his brain went straight to autopilot and he scrambled to his feet, lunging for the door.
Castiel appeared in front of Dean in a flurry of wings, stopping the hunter in his tracks. Adrenaline and instincts took over and Dean sent a right hook flying towards the angel's face with all his strength. He felt it as the bones shattered, but the physical pain was nothing compared to the pain of betrayal he felt as he slumped to the floor at Cas's feet.
"I don't get it." Dean finally pushed out. It was barely a whisper, but both angels still heard it. "Cas... you- you Fell. You're human now..."
"Dean..." The amount of emotion in the angel's voice, as if he was actually pained by Dean's inevitable reaction, only broke Dean more. "Angel's don't become human when they Fall. They never did."
Dean managed to lift his head and question those words with tear-filled eyes.
"When an angel Falls, their grace is cut off from Heaven." Lucifer explained, an odd cousin of pity swimming in his eyes as he looked down at the broken human. "They either wither and die, or adopt Hell's power as their own."
"Who did you think Azazel was, Dean?" Cas asked gently.
"He was one of the angels that stood with me in my defiance against God. As a result, he was cast out with me." Lucifer came to crouch down beside Dean, who averted his eyes almost immediately.
"He-" Dean's voice cracked instantly, but he still forced the words out as he bore a hole into the ground with his stare, "he was a demon..."
"Not quite. He was a Fallen Angel. Exactly like Castiel." Lucifer gestured with his head up at his brother and Dean's gaze was once again drawn to seek solace and strength in the angel's impossibly blue eyes. But what met Dean was a filmy yellow that was all too familiar, but looked all too wrong on Jimmy Novak's face. Cas blinked the demon eyes away, and startling blue once again reigned.
"When...?" Dean managed to choke out through his new nauseating wave of horror.
"Since the very beginning." Cas answered quietly; not apologetic, but sympathetic enough to make Dean's stomach turn.
"He's been one of my most loyal brothers since the beginning of times." Lucifer confirmed, glancing up at Cas with something akin to brotherly affection in his eyes. "It seems only fitting. Sam, the boy with the demon blood, was befriended by a demon in my services. It only makes sense that Dean Winchester, the Righteous Man, was befriended by an angel with the same cause. It's only because of your faith in Castiel that he ever managed to convince Sam to say yes. So I guess I owe you a thank you as well."
Lucifer stood without another glance at the human. He clapped a hand on Cas's shoulder, once again exchanging an appreciative glance, before walking away and testing his new body's range of motion.
Cas knelt down beside Dean in Lucifer's place and rested a gentle hand on Dean's shoulder in comfort. A swell of pure rage filled Dean to the brim at the careful touch, at Cas's knowledge of how to interact with the hunter, at the false care he was still maintaining.
"Dean..." Cas said, and he sounded so much like the friend that Dean had trusted with his life, and more importantly, Sam's, that Dean's mind went completely blank with full blown fury.
The next thing he knew, an angel blade was shoved to the hilt into Cas's chest, Dean's hand wrapped around it in a white knuckled grip. The blue eyes widened in shock and pain and a gasp escaped the Fallen Angel before he fell back.
Lucifer turned on his heels just in time to watch the bright light burn out and Castiel's vessel crash to the ground, the blade still deep in his chest.
"NO!" He cried, sliding to his brother's side. He lifted the vessel almost desperately, resting it's head on his lap and touching the face as if he expected the angel to wake up. But it was too late.
Dean was numb as Lucifer turned impossibly icy blue eyes on him, raised a hand, and clicked his fingers together. Dean Winchester knew no more.
A/N: I'm sorry.