Author's note: I don't own, I forget that sometimes :( Spoilers 11x14 "The Vessel". Sorry!
Update: I hope it is much better! Huge thanks to amazing AlexHamato for making this story readable and for giving me so many wonderful ideas!
There was irony that the mind of a heavenly creature that lived thousands of years was an empty white room.
However, this was just a little piece of his own mind (or his vessel, he could no longer tell where the difference was). The same small corner where Lucifer had dragged him and beaten him up, after Cas didn't allowed him to kill Sam.
The sensation was surprisingly physical. He could taste the blood from his split lip. His pulse was pounding fast in his temples. Chills crawled over his crushed body.
The archangel was furious.
While Lucifer approached him, Castiel felt how the fear grabbed him by the throat.
"You cost me my cover and the weapon. And you know how hard was for me to get it." A wicked grin cracked through the anger as Lucifer smiled seductively. "And on top of that, you spoiled all the fun. Right when I was about to smear Sammy's guts all over the walls of their sweet home. You had to pay for that, little brother."
The blood was bright against the white walls. The angel was crouched on the floor, with his knees pressed tightly to his chest.
Preventing the devil from killing the young Winchester had drained all his strength. He didn't even try to defend himself as his brother hit him. Or maybe he didn't want to fight back. Part of him accepted the beatings as some kind of a twisted penance.
Not that there would be a difference. Even with his full powers Cas was unable to resist the archangel, let alone Lucifer.
"Castiel." The archangel shook his head with mournful expression. "What am I going to do with you?"
In his mind, the Satan was the spitting image of his first vessel, Nick, but without the damage his Grace had caused. Lucifer stood leaning over the collapsed angel, the devil's hands still sticky by drying blood.
"Answer me!" The voice echoed loudly in the empty room.
Castiel winced and shrank back.
"You know, this isn't fun at all." Lucifer continued with a calmer tone, but still there were angry notes below the surface. "However, I can beat you whenever I want. And it's not like you fight back. It's like I'm hitting a dead cat."
He stood up and wiped his bloody hands on his shirt.
"I don't understand your misplaced loyalty to the Winchesters. They just threw your ass in Australia, along with mine."
Cas swallowed hard. Blood was gathered in his mouth. Sparks of desire to protect Sam and Dean flashed inside him, but he knew it was pointless. He didn't want to participate in his fallen brother's mental games.
"I really don't understand," he continued, "I played you for a long time, I know how they treat you. For them, you are just a tool. Now you are broken. And you know what happens with the broken tools, right?"
Castiel didn't answer, only pressed his forehead more tightly to his knees.
"After all this nonsense about family and stuff like that, they don't even notice it isn't you."
The angel flinched and Lucifer smiled triumphantly.
"I mean, it's been weeks, and I'm not that good actor. Someone had to figured it out."
Castiel felt the archangel's Grace. It was something like being inside the burning iceberg, pressed and surrounded by cold, bright white flames. And it ached. The pain had nothing to do with the vessel, it was as if icy fingers were clutching his true form, dug its nails into him, tearing him slowly and painfully apart.
"So, tell me, what do you owe these hairless apes?" Lucifer asked with a mockingly thoughtful expression.
Cas suppressed his strong desire to tell him not to call the boys that.
"You know that Dean is grateful that you said yes, instead of his precious brother."
Actually, it was one of the reasons Castiel said yes in a first place. He knew they needed Lucifer. Also he knew that Dean couldn't bear to lose his brother again.
"For those two, the whole world is just a collateral damage. Why do you think you'll be something more?"
Despite his weakened state, the words came out of his broken lips before he could stop them. "Do not want to be... more." Castiel's voice was low and raspy, his mouth full of blood.
He didn't look up to meet archangel's gaze.
"Oh, of course you want more," the Devil said mockingly, "You want friendship and family. You want to fit in. Don't forget that I'm in your head, little brother. You think that if you are useful enough to them, they will accept you as an equal. But the only way to be one of them is to be born Winchester."
The Devil leaned over him and forcibly lifted his chin while Castiel's blue eyes met his.
"You know I'll kill them, right?" he said flatly, as if announcing something obvious.
The angel tried to pull away of his touch, but he was too exhausted. However, he managed to say a clearly distinguishable, "No."
"Really?" Lucifer smirked, "and why is that?"
"I'll... expel you," Cas said with a firm determination in his weak voice.
"No offense, little brother, but now you are neither in position nor able to fight me."
Cas tried again to free himself from the iron grip, but the Devil's fingers only tightened, holding his head upright. He looked away from the fierce flames smoldering in the gaze of the archangel.
"Let me tell you how things will play out," Lucifer said slowly, as if explaining to a child. "I'll deal with our dear aunt. Then comes the Winchesters, I'll make Dean to watch how I'm tearing Sammy apart, piece by piece; I'll make him pray on his knees to kill him. And when I get bored, I'll make you watch me carving my name on every piece of skin on Dean Winchester's body. When that has bored me, I will snap their necks… or scatter them to atoms. I don't know, I'll think of something. Then you and I will stay together for eternity."
Lucifer leaned forward and the angel, with horror, felt the cold breath in his ear when the devil whispered, "If you are a good boy and you are sitting quietly, I will allow you to say goodbye."