N.B.: After the last episodes, I found myself with this story idea, and it wouldn't leave me alone. So here it is on its enitirety. (It's now two parts.)

Demons

For what seemed like the thousandth time in five seconds, Castiel told himself it should have worked.

He might have been weakened since restoring his lost grace, but he had put out enough power to disintegrate all the demons in the immediate vicinity. So what had gone wrong?

And why had the sigils failed? Even if his blast wasn't enough, the sigils should have kept them out. Cas remembered the smell of burning blood and charred wood, and saw the sigils burst into flame. Had the demons used magic?

Despite Cas killing only seventy five percent of Beelzebub's demon foot soldiers with his power, he'd used himself to the limit, and he collapsed helplessly to the floor, unable to even hold himself up and battling to stay conscious. He watched helplessly as Sam and Dean fought the remaining demons. They were not your average ones either, Dean had described them as 'roided up motherfuckers', which may have been the best explanation, epithet aside. Despite all the skill, experience, and preparation of the Winchesters, everything that could go wrong did go wrong.

Sam died first, but at least it was quick. Cas, his head swimming as he fought to remain conscious and get off the floor, saw it happen. Sam decided to leave the demon fighting to Dean, deeper in the house, and went to restore the warding sigil on the door. It was a smart move, and really the only move, as rebuilt it would have kept the demons out. Sadly, the demons knew it too, and he was half way done when a machete was thrust through the door, cleaving the symbol and Sam's head in a single blow. Cas saw his soul snuff out like a blown out candle flame. It happened too fast for him to feel pain, or know he was dead at all. By the time his body hit the floor, he'd been dead for at least ten seconds. That turned out to be the night's only mercy.

Well, no. Another mercy was Dean never knew. He was in another part of the house, fighting the demons who were coming in the back. Dean was being himself, meaning he'd bitten off way more than he could chew, but he was refusing to even entertain the thought. In purgatory, this bizarre, contradictory mindset had kept him alive. He never acknowledged he was beaten; in his mind, there was no way he couldn't win, and that became a self-fulfilling prophecy. Cas loved that, that can do spirit in the face of vastly overwhelming odds. It was so illogical, and so human. In other words, perfectly Dean. It had served him well for so long, but at some point it would fail, simply because it had to. And that time was tonight.

Again, like purgatory, Dean ignored the first few injuries, even though the one to the back of his leg hampered his movement. But he kept fighting, because that's what he did, and it was all he could do, save for give up and be torn apart. He was giving as good as he was getting, at least for a while. But he was human, and they were demon, and they had numbers. One of them also had a gun.

Cas had managed to pull himself back up to his feet using the wall when he heard the first gunshot, and his heart sunk, because it didn't sound like one of Dean's guns. And how long had he been with the Winchesters that he knew what their guns sounded like? But he was sure.

By the time he stumbled to the kitchen, the remaining demons had Dean down on a kitchen table, stabbing him like he was a particularly troublesome roast. Cas had no energy to smite them, but he had his angel blade, and he started stabbing them as rapidly and desperately as he could. While exhausted, seeing Dean like that gave him a surge of anger that seemed to hold him up.

He killed three before they attacked him, and he felt a blade sink between his ribs as they pinned him to the wall and started battering him with punches. Still, even though he had wasted most of his grace, it wasn't enough to truly hurt him. They were damaging his meat suit, but not enough to kill him.

He struggled and attempted to fight them off, but they were so strong it seemed like a lost cause. Until the one who had stabbed him had his head explode, and Cas recognized that gunshot sound. Dean wasn't dead yet, and he had shot the demon. Technically, a head shot wouldn't kill a demon. But this one had taken off the top of the skull, and the meat suit was unusable, so it smoked out.

He and Dean managed to kill those left in the kitchen, but when Cas finally saw Dean, he could've cried. He'd been shot in the torso, leaving a ragged hole close to his solar plexus, and he was swimming in blood. It covered the kitchen table and pooled on the floor. He shouldn't have been able to stand, but he was leaning against the table, blood pouring down his front, from the gunshot wound, from the various stab wounds, from his nose, from his mouth. He was somehow conscious, but barely, his green eyes glazing over even as he tried to fight it back. Dean seemed to spend most of his life fighting something or other, even if it was himself. He tried to form words, but it took him a moment. "S-Sam," he gasped. It sounded like a question.

There were noises outside, and Cas could see the shapes, the dark movement. More were coming, and they couldn't fight them back. "He's all right," Cas lied, put his arm around Dean's shoulders and helping him out of the kitchen. He all but dragged him into the nearest room, where the sigils seemed to be still intact. Apparently they only concerned themselves with the ones on the front or back door.

Dean had no ability to stand on his own. They were barely inside when he collapsed, Cas catching him and lowering him down to the floor. He was sopped, a blood sponge, leaving a huge crimson trail. Cas sat back against the door, a bloody Dean across his lap. He shouldn't have been conscious, but Dean was fighting so hard. He was dying. He'd lost too much blood. Even if Cas could get a signal on a cell phone, no ambulance would have arrived in time. And Cas had no energy to heal him. He tried, he attempted to dredge up what little power he had, but the end result was nothing. Mentally he sent out an S.O.S. on angel radio, asking for anyone to help him, but no angel responded. And why would they? Most angels didn't consider him their brother anymore.

Dean was shuddering now, shock sinking its claws deep, but he was still fighting to stay with him. His brave, stubborn soldier, refusing to acknowledge he was doomed. "You look after him," Dean said, his voice thick with the blood in his mouth. A small bubble of it former at the corner of his lips. "You take care of him, Cas. Promise me."

"Dean –" Cas didn't want to cry. He was an angel, not a human anymore, but he felt the tears forming regardless. It felt like something was forming in his throat, clogging it.

"Promise me." He was struggling to breathe. There was a gurgle in his lungs.

Cas looked down at Dean, stroking his bloody hair. Dean was crying too, tears mingling with the blood running down his face, diluting it. How did humans hold so much blood, and how could they lose it so fast? He was in pain as well, trying not to show it, but it was obvious. Cas felt so helpless. He couldn't heal him, couldn't ease his pain, all he could do was watch him die. "Of course," he said, aware that lying to him was the only pain relief he could give him. Let him think Sam survived. Knowing the truth would hurt him more.

Cas heard demons in the house, coming for them. He wondered how long the sigil would hold, or if whoever threw the spell was preparing to throw it again.

Cas put a hand on Dean's forehead, and using the last bits of dredged up energy, he was able to plant an image in Dean's mind, show him his heaven, so he would be at peace. He relaxed with a sigh, and finally, Dean died, his soul finally flickering out.

Cas's stab wound was throbbing, but it didn't hurt nearly as much as this did. It felt like all his internal organs – stomach, spleen, lungs, liver – contracted into a single solid fist that tangled up his stomach until it felt like he was about to burst. The noise of the demons behind the door abated, because they only wanted the one Winchester still living. They had no interest in a powerless angel. They knew it was more agonizing to keep him alive.

What was he supposed to do now? He couldn't return to Heaven; he wasn't wanted there. But now there was nothing left on Earth for him either. Sam and Dean were his family, and they were so much blood on his hands. Cas felt like screaming, as if it would do any good.

"This is exactly what's going to happen," a voice said. "If not this way, in a similar way. They will leave you behind, Castial."

It took him a moment to understand. He was no longer alone in the room, and Dean's corpse was no longer on his legs, although Cas was still covered in his blood. The room had shifted as well. There used to be a window, but now there wasn't. It had been dark, and the shadows of furniture had haunted the room. Now it was bright and empty, save for a copy of himself looking at him.

Although no, it wasn't himself. It was Lucifer, looking like him.

Castiel's mind reeled, as he tried to make sense of it all, and he angrily wiped the tears from his face. How did this make sense? Beelzebub was released when Lucifer's cage cracked, and while the Darkness was eating up the majority of their time, Beelzebub was growing his demon army, waiting to strike. He wanted to take what he could of humanity before storming the gates of Hell, and before the Darkness wiped out humanity. He wanted to be settled elsewhere before the bloodletting started.

Except, no. The part about the Darkness was real. But the rest of it hadn't happened. Why did he think it was true? Suddenly he remembered agreeing to be Lucifer's vessel, so he could stop the Darkness. He also remembered watching the Winchesters die a thousand times, in a thousand different ways.

Weakness was replaced by rage, as Cas looked up at Lucifer, wearing his – formerly Jimmy Novak's – form. "Why are you doing this? What is the point of torturing me?"

"I'm not torturing you, Castiel. I'm trying to make you understand something."

Not real. Sam and Dean were still alive. He would have been relieved, except Lucifer was here, and that didn't seem to be cause for a celebration. "That you're an evil bastard? I know that already."

Lucifer smirked. It looked weird, seeing such a gloating expression on his own face. It didn't look like it quite fit. "The Winchesters have influenced your vocabulary, I see. Cute. No, Castiel, I want you to remember who you are."

Cas stood, now that he knew the feeling of weakness was just an illusion. Kind of. He did feel like a shadow of his former self, even though he knew now this was all happening inside his own head. He was not the boss here, though. Lucifer was an archangel, and if wanted to overpower Castiel, he could without difficulty. It was probably the only thing keeping Cas from acting against him right now, beating in his smug face. "I know what I am."

Lucifer shook his head. "No, I don't think you do."

"I'm an angel."

"A poor example of one. That's what you were going to add, weren't you? I think you're wrong."

"Which part?" Cas didn't know why he was allowing Lucifer to bait him into this conversation. No good could come of it. But he was something of a captive audience.

That smirk again. He took a step back, cocked his hip, crossed his arms over his chest. His body language was cocky and assured. No one needed to tell him he ruled this place. "The poor example part. Although, beyond a shadow of a doubt, you are majorly fucked up."

"Tell me something I don't know."

"You're an elephant in love with an ant."

That statement baffled Cas into several seconds of silence. Was Lucifer being surrealist with him? He barely understood it as an art movement. Used in conversation, Cas had no hope of following. "What?"

"How old are you, Castiel? No, don't answer, I think that will lead us into unnecessary conversational cul de sacs. I know you're younger than me, but about as old as Earth, correct? Let's just consider all your lives at this point as one uninterrupted thing, okay?"

Cas shook his head. He couldn't even guess where this was going. "Are you trying to confuse me?"

Lucifer rolled his eyes and sigh, letting his arms fall to his sides. Only now did Cas realize that while Lucifer was wearing a dark suit and his trench coat, Cas himself was now clad only in the white scrubs he wore at the mental hospital. At least he was no longer drenched in Dean's blood. "I'm making a point. Assuming the Winchesters somehow, miraculously live to say, one hundred – which, come on, they'll be lucky to live out the year, but let's be generous – how much is a hundred years to you? It's too short to even be a blink in your existence. It's half a blink. A twitch."

Cas thought he understood now, although he didn't like what he was saying.

Lucifer suddenly pointed at him, and Cas wondered if his eyes had always been that blue, or if Lucifer was heightening it for effect. "Humans are mayflies to us. Tides of their lives wash in and out, a hundred thousand times, a million. Why would an elephant like you ever give a shit about an ant?"

"The Winchesters are not-"

"Yes, they are." Lucifer threw up her hands, as Cas realized the room had shaped itself into his room at the mental hospital. He wasn't sure if it was his unconscious doing this, or Lucifer's doing. "Castiel, do you ever stop and think what you've thrown away for these insects? You were a general, and if scuttlebutt can be trusted, a pretty good one. You could be running Heaven now, if you hadn't tried to cram your huge leathery ass in that goddamn anthill. " Lucifer scowled, and made a dismissive motion with his hand. "Yes, I know how that sounded, just go with me here."

"I don't regret helping the Winchesters. If you're trying to make me, you may as well stop. You can't do it."

Lucifer walked up to him, and grabbed him by the shoulders. His grip was firm but not painful. "But they're going to die, Cas. Sooner rather than later. And what will you have then? Heaven doesn't want you, but you have no place here. What are you gonna do?"

Cas shook his head, finding it difficult to look away from Lucifer's gaze. Even in the form of his vessel, it was strangely compelling. It was the veil of innocence, barely concealing the evil within. "I'll deal with it when it happens."

Lucifer canted his head. "Will you? Will you deal with it like this?" He gestured at the hospital room around them. "That might kill a decade or two. What then?"

Cas opened his mouth to reply, and then closed it. He didn't know what to say. He didn't like to think about it. In fact, as of late, he didn't like to think five minutes ahead of anything. Existence itself seemed onerous. The only joy he got was from watching television, or talking to Dean.

"Of course you don't know. You made a huge mistake, Castiel, and you don't know how to fix it." Lucifer stared at him, as if seeing into his mind – which he probably could do since they were sharing a vessel - and his expression morphed, from cockiness to surprise verging on disgust. "Oh no. You can't be serious."

Cas didn't know what he'd found, but he knew he didn't like it. "Do you think I give a shit about your opinion of me, Lucifer?"

"How?" Lucifer replied. This was not the first or probably the last time they had a conversation that felt like they were both discussing different things. Lucifer was quite gifted with words, and could use them to tie anyone up. "How do you even do that?"

"Do what?"

Lucifer threw up his hands and walked away, shaking his head "You're an elephant in love with an ant. I don't … wow. " He turned back to face him. "They're Dad's version of sea monkeys, you know? I still have a hard time telling them apart. And you actually love one?" He scoffed. "How do you pick one fly out of a swarm?"

"Humanity is not a collection of insects. They are better than you think."

Lucifer cocked his head, so he was looking at him with one jaundiced eye. He hardly seemed convinced. "Really? After all this time, Castiel, fighting beside and for them, have you not realized they're worse than you think?"

"Some are. Some aren't. I don't judge the many because of the few."

Lucifer widened his eyes briefly, comically, before shaking his head yet again. He snickered in a condescending way that would have been infuriating if Cas didn't feel so tired and dispirited. Maybe those fights and slaughters hadn't been real, but they felt real, and if he closed his eyes, he could feel Dean leaning on him, his blood trickling down his back like sweat. Humans had so much blood in them. "Even you're not buying your own shit anymore, Cas. But why him? You gotta tell me, 'cause I really don't get it. I mean, for a sea monkey, I guess he's not unattractive, but ugh. That personality. Can you say Daddy issues and codependency? I'm pretty sure he can't."

"What do you want me from me?" Cas gritted his teeth, not wanting to give Lucifer any satisfaction. But things were probably beyond that. He was tired of the mind games, of the questions with no point, and his rants against humanity. Lucifer had to know by now that Cas was never going to be one of his converts, so he was probably doing it simply because he was bored. Agreeing to be Lucifer's vessel also meant agreeing to be his entertainment, which hadn't occurred to him at the time. Maybe if he had known that, he'd have accepted death instead.

"I just want to know how an angel, a celestial being of divine intent, falls in love with a sad sick piece of shit like Dean Winchester. Walk me through it. When did it happen? Why? How? Let's start with the last question first."

Cas frowned at him, and decided to walk away. He knew Lucifer wouldn't let him go if he wasn't done with him, so Cas simply sat down on his bed, that one that had been his home last time he had Lucifer in his head. This time, it was much worse. Lucifer stood at the end of the bed, now wearing a nurse's cap tilted at a jaunty angle. "Does this make you feel better, mocking me? Get in line."

Lucifer sat on the edge of his bed, and clapped a hand on his leg. He probably thought it was friendly. He was giving him a cheesy smile that Cas didn't trust one bit. "I'm not mocking you. Okay, a little, but mainly I'm just curious. We should be friends, Castiel."

Cas snorted, amused for once.

"I'm serious. We've both rebelled against Heaven. It made me infamous, and it made you pathetic, but hey, we can't control other beings reaction to us, right? Well, sometimes we can. Depends on the being. But we should be united. We have more in common than we do differences, in spite of your weird human fetish." He shuddered in mock disgust.

Cas fixed him with his hardest look. Part of him knew he should indulge Lucifer, get on his good side, but he knew that ultimately, he didn't have a good side. He may have agreed to be his vessel, but not his friend, or even a passing acquaintance. Maybe Cas was now the standard for rebellious angels, but he was nothing next to Lucifer. Contempt was too small a word for his feeling about him. "You killed me once."

Lucifer held up his hands in a shrug. "So? Dad brought you back. No use crying over exploded milk."

Lucifer probably thought he was funny. The fact that this made him somewhat human wasn't an irony lost on Cas.

"You want to go back home, right? Cas, don't you get it? You're coming to your senses. Whatever thing you had for Dean-" Lucifer shuddered again. "-you finally realized that was a mistake. The human world isn't for you. Humanity isn't for you. You're better than all of them. And if you really wanted Dean, well, fuck it. You can have a hundred of them, a thousand. You can make your own slave army of Dean Winchesters if that's your thing. We can take Heaven, and fix it. Dad is gone, and he's not coming back. You know it and I know it. Isn't it time for the angels to fight for themselves instead of kowtowing to those worthless mud monkeys?"

Cas closed his eyes, and sighed. This was how Lucifer got to you. He said things that almost made sense, wrapped around a whole lot of ugly. That sick weariness he had felt since recovering from Rowena's attack dog spell still lingered, and for a while he thought maybe it was some kind of mystical backlash, but since it was still bothering him, even deep inside his own head, he knew it was something else. He was so tired of fighting his own people, something in him didn't even want to fight Lucifer, even though he really wasn't one of them anymore. Lucifer was more demon and angel, but he was the only one who didn't seem to realize that. After a moment, Cas opened his eyes. "Do you know why I said yes to you?"

Lucifer nodded. "To kill the Darkness."

"That was part of it. But I said yes to you knowing, when your job is done, Sam and Dean will destroy you. They beat you once. They will beat you again."

Lucifer's eyes narrowed, and turned hard. Cas would almost swear he saw blue flames flickering deep within his pupils. "If they can manage to hurt me, they'll be killing you too."

Cas nodded. "I know." Maybe their father had been bringing him back as punishment. Cas hoped that, if he helped expel the Darkness, maybe he'd let him rest this time. He'd earned it, hadn't he? He'd done his best to protect humanity, to protect Dean and Sam, and he had failed so many times. He was ready to be done. The Winchesters didn't need him; Heaven didn't need him. Now Cas didn't even need his own existence. He was so very tired.

Lucifer stared at him, seemingly shocked as he stood up, studying Cas like a fascinating new species of insect he found in his sandwich. "Holy shit. I don't even need to break you, do I? You're broken."

Cas imagined there was one of those small, weird portable television sets on the bed, and there it was. He didn't think Lucifer would care about such a small, inconsequential thing, and he was correct. "Think whatever you want. I don't care."

Lucifer's lip curled in disgust. "Wow. I'd feel sorry for you if you weren't such a weirdo."

Cas fiddled with the antennae, trying to get some reception. He glanced up, to see what face Lucifer was making at him now, but he was gone.

That was probably for the best. Cas really just wanted some peace. And if indulging in this was the only way to get Lucifer to leave him alone, then he was going to do it for as long as he had to. The next time the Winchesters died on him would be way too soon.

At least this television had endless channels.