A/N: I so desperately want to see this relationship in the show, and I'm probably not going to get it, so have a ficlet.
Lucifer stretched within Castiel, back arching like a cat's as his mangled wings of ice and bitterness spread wide. He mewled in contentment, the smile on his face genuine, unlike so many before it.
It had been so long. Or so it felt. Five years in Hell was nothing like the thousands he'd spent in the Cage previously, but, once he'd tasted freedom that first time? His second trip was positively awful. Not to mention Michael's ranting and raving. 'Oh, Daddy wouldn't do this to me. I'm the good son.' Please. That Deadbeat didn't care about anything but His Plan.
But Michael was gone, trapped in the Cage and left to his own misery, while he… He could finally breathe air that wasn't sulfur, dust, and decay. Claustrophobia incarnate. He could finally walk the Earth again, let the Sun's rays shine down on him. Though nowhere near the Glory of God, the tiny star in the center of the Milky Way was a balm nonetheless for him, a creature that was forced to spend eternity in darkness.
Darkness. Right. That little issue. He'd handle her sooner or later. When he felt like it. For now? First thing was first. His red-tinted eyes glanced down at the huddled seraph trying to hide in the center of his own mind. Lucifer smirked.
He approached Castiel, trueform slinking around him like a serpent of light before solidifying into a more human form, still massive even in comparison to the seraph. His smirk remained as he reached out to poke one of Castiel's many wings. Castiel flinched.
"Aw," Lucifer cooed. "Why the long face, little brother? Isn't this what you asked for?"
"You said you'd defeat the Darkness," Castiel replied, a small speck of anger leaking into his tone.
Lucifer tilted his head at the insubordination. This angel always did give him trouble. Even after Lucifer had utterly destroyed him with a snap of his fingers, Castiel still had the nerve to stand up to him. Cute. Infuriating, but cute.
"And I will," Lucifer stated. He idly looked at his claws, a habit he'd picked up from the humans. "Eventually. Thought I'd have a little fun first."
Castiel bristled, feathers puffing up in his ire. His head remained buried in his knees, however. Still not brave enough to truly face Lucifer, then. Sam was braver.
"You'd wait, as the Darkness destroys countless humans and angels - everything! - just… For what? Some-some R&R?"
"Ooh, look at you. Using human lingo properly. I'm impressed."
"Answer me!" Castiel growled.
Lucifer snapped. No one commanded him. Certainly no lowbrow angel. Castiel would learn. Or he'd suffer. Again.
His clawed hand moved quickly. It snatched Castiel's right wings and spun him around. Castiel shouted in surprise, fear finally registering on that annoying face of his. Lucifer's face now.
Castiel didn't have time to react further. Lucifer's hand wrapped around his upper body, holding him like a doll. His thumb pressed up under Castiel's chin, against his neck. Wings trapped behind him, forced to stare at Lucifer, jaw held shut, Castiel could do nothing but tremble.
"I answer to no one," Lucifer snarled. He brought Castiel closer. "Do you really think I'm going to obey you, you insignificant gnat. You, who can't even do one. thing. right. You tried to steal Sam from me, and you failed. You tried to be God, and you failed. You tried to save your species, to save Heaven, and you damned it to destruction. Nothing you do, Castiel, is right."
Lucifer smiled again, the smile of a predator. Castiel's wide, watery eyes only fueled Lucifer's disgust towards him. This angel had chosen humanity over their brethren. He had ruined everything. All of Lucifer's plans. All of God's plans. What a thorn in the side of the Universe.
"And, now, I have your body," Lucifer taunted. "I'll have your friends. I'll have everything. Because you're weak, Castiel. You put the humans before all. If you'd just left it all alone, the Darkness would have never been released. If you'd just left it all alone, let me and Michael fulfill our destinies, the Story would've ended the way it should have."
He finally released Castiel. The seraph hit the ground of his mindspace with a grunt and flutter of wings. He shook as he tried to push himself to his feet. When he raised his head to face Lucifer, he wore a glare that would frighten many. Lucifer, however, was only mildly amused.
"You're wrong," Castiel hissed, the tears on his face ignored. "I'm… I'm God's chosen. Amara said so herself. God has brought me back many times. He must have a purpose - "
"Or I inherited my sadism legitimately, and you're just a toy He loves to torture."
Lucifer shrugged nonchalantly and turned away from Castiel. Though he played indifferent, inside, Lucifer burned. He could glean from Castiel's memories that the seraph spoke the truth. He had been resurrected on more than one occasion. Destroyed by Archangel, ravaged by Leviathan, only to be brought back as good as new. Sometimes better.
His nails dug into the energy that formed his palms. Never had his Father shown such mercy towards him. Even Raphael hadn't been saved from utter destruction at Castiel's hand. Only Castiel was allowed to survive Death.
Why? Lucifer seethed. Why this pissant of an angel, this disloyal - !
Apprehension crawled up Lucifer's back. His wings shuddered, clinking lightly, at the feeling.
Gabriel. He felt Gabriel in Castiel's mind. An echo. A memory. No, not the room with the ugly, flowered wallpaper or the duct tape. Convenience store. Black jacket. Tan jeans.
Lucifer hissed, a sound that soon deepened into a growl. He whirled on Castiel, slamming his hands down on either side of the seraph. Castiel, surprisingly, didn't shriek in terror at his actions. However, eyes wide, Castiel flailed backwards. He fell. Lucifer loomed over him.
"You've seen Gabriel recently, haven't you, brother?" He demanded.
The tears were drying in Castiel's eyes. "No."
"You lie. I'm in your head, Castiel. I know you've seen him. Now, you might understand why that fact comes as a surprise...considering I killed him. Where's the little vagrant hiding? I'd like to pay him a visit."
"I don't know."
"I. Don't. Know," Castiel bit back.
He held his head proud, despite how close Lucifer was. Close enough to devour. Oh, if only he didn't depend on Castiel's body to tether him to Earth. If only there wasn't some bullshit clause in the Universe that kept him from being like the demons he'd sired. He'd burn through Castiel. He'd tear through him until he got the answers he sought. So much perfect pain he knew how to inflict...and he couldn't.
Castiel feared him. He wreaked of the scent, his thoughts screamed it. But there was that faith. That blind faith in something greater that gave him the bravery to bolster himself against Lucifer. Even when he didn't believe in God, he believed in something.
Lucifer hated it. He hated the sentiment in Castiel. He hated the sentiment in Sam. Time and time again it was used against him. What a joke. There was nothing greater. Not for them. They would die. The end. Fools. Weak little fools.
The corner of Lucifer's lip twitched. Castiel told the truth. He pushed himself away from Castiel, reining in the fury that fueled him. His bitterness. A dark smile spread across his face. He tutted.
"Castiel," he drawled. "Castiel, Castiel, Castiel. You know I only want his help."
"You said you could defeat the Darkness yourself," Castiel frowned as he stood.
"I. can," Lucifer stressed. He rolled his eyes. "I'm growing tired of saying that. However… Two Archangels are better than one, and the quicker the fight with the Darkness is, the less destruction results. Don't you want that, Castiel? More of your poor, pitiful planet surviving. Your humans."
Castiel narrowed his eyes up at him. Such a frequent expression on the seraph's face. On his true form, it wasn't as endearing. Castiel squared his shoulders.
"You lie," he stated. "You forget, Lucifer, that occupying my mind is a two-way street. After all, I'm still an angel. Reading minds is something I do. You don't want Gabriel's help, you want to remove him from the picture. Again. Because he poses a threat to you. He could throw you back in the Cage. He could release Michael."
Lucifer scoffed, cutting off what would be a lengthy rant if allowed to continue. He had let down his guard for a moment, in his rage, and Castiel had been allowed to glean his intentions. Big deal. He was much better at hiding his deeper thoughts and wishes from Castiel than the seraph knew. He'd perfected such a technique long before Castiel had even been created. One slip-up was only a nuisance, any further threat nonexistent.
"So I want to save my own skin. My original point still stands, Castiel. Gabriel could be useful." He smirked. "And you can't stop me from hunting him down."
Castiel's jaw clenched with his fists. He glared at Lucifer with hatred.
Camaraderie had been struck between Gabriel and Castiel, even though Gabriel had deceived him. Interesting. Though Lucifer admired the loyalty, he wouldn't risk being caged again. He knew where Gabriel stood, and it wasn't with him. A shame.
"You'll lose," Castiel said, sudden and with conviction.
Lucifer's smirk dimmed. "Beg pardon."
"I'm not the only failure here, Lucifer. In everything you've ever done, you've lost. The War against Heaven found you locked in a Cage. The Apocalypse, again, found you locked in a Cage. In the end… You lose."
"Oh, I think I'll win."
"And that's the problem. Your arrogance. Your ego. You're so caught up in the idea that you're perfect that you can't see how far you've fallen. You may have been the brightest and strongest at one point, Lucifer, but now? Your Grace is tainted, your wings shredded. The darkness has corrupted you. Amara wouldn't even think to consume me because she said I was 'used up.' I wonder what she'll think of you if you face her now?"
Lucifer didn't reply. Very few times in his long life had he found himself speechless, most at the hands of Gabriel, yet here he was, guarded gaze bearing down on the little seraph that really should know by now not to open his infernal mouth.
A monster. Great big bag o' dicks. Old dog with old tricks. Broken. Corrupted. Fallen. Predictable. Evil. All his fault.
No. He was perfection. Everything he did would be perfect. He would rule a perfect world. He was made to be the best. He would be.
"Cas. Hey, Cas? ...Hell-ooo?" Fingers snapped near his nose. "Earth to the angel."
Lucifer looked away from the wall he'd been staring at to focus on Dean Winchester's face. So smug. Just like Michael. How irritating.
"Something about that wall more interestin' than getting 'the hell out of Hell,' or?" Dean sassed, though worry shone in his features.
If only you knew how much I want to snap your neck.
I won't let you.
You have no say in the matter.
"No," he replied, his voice Castiel's. "I was just thinking."
"Okay, well, wanna clue me in? Because you zoned out for a good few seconds." Dean frowned. "You sure you're alright, man? That fight with Lucifer - "
"I'm fine." The smile that stretched his lips felt foreign, not like Nick's. The hand he placed on Dean's shoulder was tanner than he was used to. "Everything's going to be fine, Dean."