A/N: Okay everyone, prepare yourself for an angst fest.

This idea just came out of the blue and I wrote this story in like two weeks. This is set in a kinda of AU version of the S6 finale/ S7 opener. It's kind of a mash up of it. Cas hasn't gone full-blown Gostiel, but Sam and Dean still know he's betrayed them, and he goes to put the souls back in Purgatory sooner. There's also no Leviathans-just the power of the souls that is corrupting Cas but he's not totally cracked. And Sam's wall is still broken as you will see, but he hasn't gotten out of the panic room yet. So yeah, kind of confusing mash up of events, it's not hard to follow along with the story though, so I hope you enjoy it ^_^

There's also A LOT of Greek Mythology and other mythology thrown in, like mythology about fallen angels, and the Grigori which were kinda mentioned in Supernatural in "Angel Heart" but I'm going with the mythology I found on them in this story, so lots of AU mythology stuff going on.

Anyway, I'll let you read now...

Katabasis

A Supernatural Fanfic

Chapter One

Apolia

(Ruin, Loss, Destruction—Perdition)

Castiel glanced down at his hands with resignation. The sores were breaking out all over his vessel now as the souls he had consumed burned him from the inside. He didn't have much more time left on this earth, but somehow all he could find in himself to do was feel regret.

Regret for betraying the Winchesters as he had, regret for being the cause of a civil war in Heaven, regret for having to kill countless of his brothers and sisters because they had left him no choice. Regret for breaking Sam's wall and sending him into a coma, trapped in his own memories of Hell. Regret for the look on Dean's face; first when he had still been holding onto one scrap of hope that Sam and Bobby were not right about Castiel's betrayal, and then the betrayal itself when the hunter had found out it was all true after all.

Regret that he was even still alive at all.

Castiel had made peace with his death; at this point, after everything he had gone through, everything he had done, he welcomed it.

But not quite yet. He still had to try to fix what he had done, and that started with curing his friend of the ailment he himself had caused.

Flight was difficult. The souls were burning through his true form as well as his vessel, eating up anything he had to offer. But he managed to get to Bobby Singer's house. It was warded against angels, but not all of it was sound and he was able to get in anyway. Bobby was slumped over his desk with a half drunk bottle of whisky, having put himself into a drunken stupor. Castiel didn't see Dean anywhere, but figured he was out in the scrap yard somewhere, drinking his own sorrows away alone, the way he liked best.

As pain at the knowledge that he had caused his dearest friends' suffering ate at his insides like the souls already consuming him, he made his way to the panic room where Sam was lying on the small cot, still but for some minute twitches every once in a while. His eyes roved constantly under his closed lids, dreaming or perhaps simply caught in indescribable memories.

Castiel crouched next to the cot and reached out, touching Sam's forehead and forcing what little power he had left into him, building the crumbled wall back up.

He had intended on coming and going without knowledge, but Sam gasped and his eyes flew open as soon as Castiel had finished the healing. The younger Winchester surged upright into a sitting position, looking around and breathing heavily. Finally his eyes fell on Castiel.

"Cas?" he asked breathlessly, eyes narrowing. "W-What's going on?"

The angel straightened up and held out his hands. "I only came to heal you, Sam," he said.

"I'm not…" Sam began then frowned. "Cas, you look….terrible. What happened?"

"It's…the souls I took on," Castiel told him, glancing down at his corroded hands. "I—I am going to get rid of them now. Put them back into Purgatory. I just…wanted to heal you before I did. And say how sorry I was. For everything."

He turned away then, but Sam pushed himself shakily to his feet and grabbed Castiel's shoulder before he could leave. Castiel winced, Sam's heavy grip digging unknowingly into more lesions on his body.

"Cas, wait," he pleaded, moving so he could look the angel in the eyes. "Let us help you. We can fix this together."

For a moment, Castiel wanted nothing more than what Sam was suggesting. To be able to work with the Winchesters one more time, to be able to fix this. To be able to make up for what he had done…but it was not to be. It would never be the same between them again anyway. Even if Sam was now offering to work with him, Castiel knew in his heart that Dean would never forgive him. He may have been the last to believe that Castiel was truly betraying them, but he would be the last to forgive him too. And Castiel didn't have the time to wait for Dean's apology now. He didn't have the time to stand around here talking either.

"Sam, this whole thing is my mess and mine alone," he told the younger Winchester firmly. "I must fix this myself."

And with that, he shook off Sam's grip and headed toward the door. "Goodbye, Sam," he said, his voice full of all the regret he had been feeling earlier.

He didn't stick around long enough to hear any protests Sam might have had, he just flew outside, reappearing somewhere deep in the scrap yard, moonlight beaming down on him. It was oddly beautiful despite his troubled soul, and he decided that he would enjoy it for a little while. He was lucky, he supposed, to be able to die on a night that was so beautiful.

Of course, he wasn't alone. Dean was sitting on the ground against the side of a beat up old car, a bottle of whisky between his feet, his arms resting across his knees. They both noticed each other at the same time, and by then, it was too late for Castiel to retreat. Of course he could simply disappear, but the weakest part of him, the part that had led him to fall to begin with, wanted to give his friend more than that. After everything, he thought he at least owed Dean a goodbye. Perhaps it would help him to understand why Castiel was doing what he was about to do. Why he had to die. Maybe then, Dean wouldn't take it so hard. Because somehow, Dean would blame himself. Castiel knew he always did, and he would with this too, despite his current anger.

"What the hell are you doing here?" Dean slurred, not bothering to move his position.

"I didn't come to make trouble, I only came to heal Sam," Castiel told him, trying to keep most of the emotions that were threatening to boil over out of his voice. "He will be fine now. And I just wanted to tell you—"

"Save it," Dean cut in, a bitter tone in his voice as he glanced up to meet Castiel's eyes. "I don't want your apology. It's not gonna fix a thing now. What's done is done, Cas. We're done."

"Dean, I—"

"Consider yourself lucky," Dean continued coldly. "Any other guy who pulled crap like that would be six feet under right now. It's only because we were friends that I'm not sticking an angel blade in your heart right now. So save your apologies, and your excuses. I don't want to hear them." He hauled himself to his feet, staggering slightly as he picked up his bottle.

Castiel swallowed hard. Dean's words hurt more than the angel blade the hunter had threatened him with ever could. But he knew that he deserved them too.

"I understand," he said softly, as Dean began to walk away. He hesitated, wanting to say more, to try to apologize again, but he knew Dean wouldn't care, so he just said, "Goodbye, Dean," and tried to put the apology he couldn't say in those two words.

And then he disappeared.

If he had stayed there another minute, he would have seen Dean turn around at that goodbye, but Castiel was already long gone, trying to make peace with the fact that he would never see his dearest friends again.

Cas disappeared. Dean still wished he wouldn't do that, but he should have known. Hell, he had pretty much done his best to make him feel unwelcome, after all, refusing to let him apologize. But still, there had been something about that goodbye…it just seemed so final. Dean had turned, lips parted to say something, anything, that wouldn't come out of his throat. Truthfully, he didn't know what to say. Try to convince Cas to stay? Why would he? Dean had made it clear to the angel that he was no longer wanted. And yet still, Dean found himself unable to just throw away a friendship like that. After all, he had fought countless enemies at Cas' side, and you didn't just give up on someone like that, did you?

Grunting in exasperation, he turned back toward the house. He was still roiling with emotions that he couldn't quite name—well, betrayal came out on top of the list. Part of him wanted to accept Cas back as his friend again—hell, he'd only recently told the angel he was like a brother to him. But then he found out about the lying, the working with Crowley, and after what had happened with Lisa and Ben…Even if Cas hadn't been directly responsible for that, it was still because of him that Crowley had taken them to get Dean out of the way. If they had been killed…Dean never would have forgiven Cas, wouldn't have even considered it. He would have killed him on the spot. Even if he'd also never be able to forgive himself for killing someone he had considered his best friend.

Of course, the fact that the angel had broken Sam's head didn't make it any better.

Sam.

Cas had said he'd come to cure him? Dean wondered if that was true, and started to pick up his pace back toward the house.

He saw for himself a few seconds later when his brother came hurtling around a stack of crushed cars with Bobby hollering somewhere behind him.

"Sammy?!" Dean cried, running a few steps forward, dropping his bottle of whisky, as he grabbed Sam by the shoulders when his brother practically tripped over his own feet. "What the hell?"

"Dean," Sam said, breathlessly, looking around. "Did…did you see Cas?"

Dean frowned. "Uh, yeah, he was here a couple minutes ago, what—"

"Where is he?" Sam asked, his voice holding a frantic note.

"Dude, slow down," Dean demanded, leaning closer to peer into his brother's pupils. They were slightly dilated, but that could just be the dark. "Are you even okay? I mean, you just got vertical, what happened?"

"Cas came and he fixed me," Sam said, a frown between his brows. "Then…he said…he said he was going to 'fix this'—what he did. He said goodbye. Dean, I think…"

"Yeah, me too," Dean agreed instantly without letting Sam finish his thought. But he'd heard the finality in Cas' goodbye as well. A cold feeling was welling up in his gut.

"I think he's gonna do something stupid," Sam insisted.

"I know."

"So, we stop him!" Sam cried, holding his hands out incredulously. "Come on, Dean!"

"It's his mess," Dean said quickly, though without as much fire as he had intended. "If he wants to clean it up, let him."

"Dean," Sam coaxed, shaking his head. "It's Cas. After everything…sure there was bad, but there's been bad blood between us too and you never left me when the stakes were high. We can't leave Cas either."

"He broke your head!"

"He pulled me out of Hell," Sam replied firmly.

"Soulless!"

"But he didn't know! Come on, Dean, are we really gonna let him do this alone? It's Cas!"

Dean looked away, ran a hand wearily down his face, feeling the scrape of stubble along his jaw, before he shook his head. "Okay, fine. But we don't even know where he is."

"Yes we do," Sam said. "I think he's going back to the laboratory he and Crowley did all the spell work in before. They had all the stuff they needed there."

"Sam, you just got on your feet again," Dean protested half-heartedly. "Maybe Bobby and I…"

"I'm coming," Sam said with little room for argument.

Dean clenched his jaw, but finally shook his head. "Fine. Let's get ready then."

He started to turn back to the house, but instead impulsively turned toward his brother and yanked him into a swift embrace. Sam stood, surprised for a moment, then wrapped his arms tightly around Dean as well.

"Glad to have you back, bitch," Dean whispered.

"Glad to be back, jerk."

Dean pulled back with a heavy sigh and forced a small humorless smile. "Now let's go get that other idiot back."

Sam smiled back and nodded.

As they came back to the house, they found Bobby standing on the front porch, arms crossed over his chest.

"What the hell is going on with you boys?" he demanded. "Sam? You okay, or what?"

"Long story, we'll tell it on the road," Sam said.

Bobby raised an eyebrow. "We goin' somewhere?"

Sam and Dean exchanged a look and Bobby heaved a sigh. "Why do I get the feeling that you two idjits are about to do something stupid?"

"Probably because we are," Dean replied.

Bobby sighed again, rolling his eyes. "I'll grab my gear then."

Castiel mixed the potion, feeling every minute pass as his heart beat weaker and his grace only fizzled and sputtered all the more. He was fast running out of time. He took the blood mixture to the wall and started painting the sigil. His hands were shaking so much that he hoped it would turn out good enough to work.

Suddenly, a tearing pain through his center folded him in half. He cried out, nearly dropping the jar of blood on the floor. He had to finish this fast. The souls were attacking his grace, tearing him apart from the inside out.

Then came inevitable footsteps running down the hallway toward him. Wearily, Castiel scrambled for his angel blade. He half expected it to be Crowley's demons, but of course, it was the Winchesters and Bobby who burst into the room. At the moment, he wasn't sure which was worse.

"Cas!" Sam cried, coming to a stop, Dean and Bobby close behind him.

Castiel glowered at them, fists clenching. He should have known they would show up, but he couldn't let them stay. Couldn't let them sway him. "You can't be here!" he insisted. "Go!"

"Cas, we just came to help," Sam said, trying to keep his voice reasonable. Castiel didn't have time for reasonable. The souls were about ready to consume him and if the hunters didn't get out of there now, Castiel feared that the blast, if he wasn't able to finish the spell in time, would kill them. Even if he were able to finish the spell, there would still be a blast. Either way, he wasn't coming back from this, but he wasn't going to let his friends die along with him.

"We know you're not planning on walking away," Dean said and Sam shot him a look. The elder brother stepped forward, a hand outstretched. "But, come on, man. You know there's always another way."

"Does that mean you'll accept my apology now?" Castiel asked him blandly.

Dean opened his mouth, but no words came out. Castiel swiftly turned and finished the sigil with shaking hands. "The repercussions of this spell will kill all of you. You have to get out of here."

"Cas, wait," Sam nearly pleaded, stepping forward.

"Go now!" Castiel shouted, pleading. He couldn't stand for his last sight on earth to be watching his friends die. It would accomplish nothing—in fact, it would go against everything he had fought this war for in the first place.

Another wave of agony overtook him and he doubled over, falling to his knees. This time the jar of blood fell from his hand, and shattered. At least he was done with that part.

"Cas," Dean said and stepped forward. He and Sam drew him to his feet, and Castiel panted, shaking, but this was a perfect opportunity.

"I said to leave," he repeated tiredly. "I'm sorry, to both of you. Goodbye."

"Cas, don't—" Dean began, but Castiel had already touched both his and Sam's foreheads, sending them outside the building. The effort of even that, sent him straight to his knees again, panting for breath, sweat beading on his skin, stinging in the open sores all over his body. He looked up at Bobby still standing there.

"Cas, you think about what you're doing here, son," the older hunter said gruffly, cautiously.

Castiel sighed as he pulled himself to his feet again. "I'm doing what needs to be done," he insisted. Why couldn't they just see that? "Go, Bobby. They'll need a level head, you know that."

The older hunter gave him a long look, then turned and left.

Castiel breathed a sigh of relief. Now he could finally finish this.

He grabbed the piece of paper with the spell written on it and started chanting. He almost couldn't get the words out as the portal started to open up, the wall cracking as it opened into another dimension.

He spat out the last words of the spell and suddenly, it felt like a lightning bolt ripped from his chest as the souls poured from his vessel, back into Purgatory where they belonged. He screamed, maybe in pain, maybe in some sort of defiance, but it didn't really matter. Because after a fraction of a second his world exploded into blinding light.

Dean didn't quite know what happened at first, all he knew was that one minute he was crouching beside Cas and the next, he was standing outside the building with Sam.

And then he knew exactly what had happened; the memory of Cas' fevered fingers touching his forehead a fraction of a second before it all went screwy.

"Son of a bitch," he ground out as he heard Sam curse under his breath.

Dean instantly surged forward, prepared to go back into the place and stop Cas if it was the last thing he did, but Sam grabbed his arm.

"Dean, wait."

"Wait?" Dean demanded, spinning around toward his brother. "You're the one who wanted to come here! Don't you tell me to wait! Cas is in there and he's gonna die!" What Dean didn't add to that was Cas was gonna die without Dean forgiving him.

Sam's expression was pained. "But Dean, think about it. If this is the only way…you saw him, man, his vessel is falling apart. The least we can do is carry on whatever fight comes next."

Dean just shook his head and marched off toward the building again anyway. "You can. You and Bobby. But you dragged me out here, and I'm not gonna let that idiot die alone."

"Dean!" Sam cried.

Just then, Bobby slammed out the door at a run, hurrying toward the brothers.

"Get out of here!" he demanded. "Dean, go!"

Dean opened his mouth to protest again, but that was when an explosion ripped through the building. Windows blew out with a bright light. It nearly sent the hunters to the ground, but somehow they all managed to keep their feet.

Dean's breath caught in his throat. As soon as the blast receded, Dean was surging forward, ignoring the cries of Sam and Bobby behind him.

Castiel took a shuddering breath and blinked his eyes open. The first thing he thought was that death looked an awful lot like the laboratory he had been in previously. Then he felt the pain, and realized that death should have no pain. Especially not for angels who weren't supposed to have any life after death anyway.

He was alive.

He was alive?

He was alive. An odd relief seeped through him. Maybe his mission wasn't over after all. Maybe now he could truly repair things up in Heaven, with the Winchesters. Maybe…maybe Dean would even forgive him eventually.

But more lights flashed, and he heard the flap of wings. He looked around to see three angels standing over him.

"Br-brothers? W-what are you doing here?" he forced from his raw throat.

The three angels wasted no time in hauling him to his feet. Castiel cried out as pain ripped through his abused body, and he could hardly find the strength to protest as they yanked his coat and tie from him, tearing the coat into small pieces and scattering them around the room. Manacles with Enochian sigils were clamped around his wrists. Not that he needed them with how weak he already was.

"What are you doing?" he croaked, his voice barely a whisper.

But one of the angels, who he recognized as Anias, answered, "Castiel, you have been tried and found guilty by the courts of Heaven. You will be subjected to the punishment most fitting for your crimes."

Castiel frowned. He was barely conscious, but something about this didn't seem right. "Tr-trial?" he inquired. "I didn't have a trial."

"The trial was concluded this morning," another angel said. "There was no reason for you to be there. No defense you could give would have changed anything. You have committed crimes against Heaven and your kin, and you will be punished for it."

Castiel felt fear seep into him. He didn't like the vague terms the angels were using. Usually, they would be a lot more explicit in a case like this. Of course, he was laboring under no delusions. Death would be his ultimate end, no matter what came before—and Castiel was sure that there would be a before.

But even after everything he had been through already, heaven's re-education and all, he had never truly expected what was to come.

"Cas!" Dean cried as he shoved through the door to the lab. He stopped short as he saw the place blown to bits.

And bits were all that was left. At first Dean felt a small tendril of hope wash over him as he didn't see Cas' body lying on the floor, but then he started looking at the bits a little closer.

"Dean!" Sam and Bobby skidded to a halt inside the door as Dean bent to retrieve a torn sleeve from a tan trench coat. His throat closed and he felt bile rising up from his stomach.

"Oh god," Sam breathed, clenching a hand in his hair as he looked around.

"Dammit," Bobby muttered, but there was sorrow in his voice too.

Dean didn't even register any of that. He bent and carefully picked up Cas' angel blade, seeing blood spattered on the hilt and knowing that his friend was gone now for good.

It was everything he could do to stay on his feet. He barely registered Sam's hand on his shoulder as they led him back outside. There was nothing else they could do here.

Castiel was disoriented by the flight, being pulled along by Anias as the three angels escorted him to wherever they were going. He thought they would take him to Heaven, but when his vision cleared and they exited the ether, he saw they were nowhere near Heaven. In fact they were still on earth, standing in front of a cliff face.

"Where are we?" he asked wearily.

It was then that a portal opened in the cliff face and two demons emerged. Castiel's breath caught in his throat, wishing he had his angel blade with him. He glanced between the other angels, but didn't see alarm or disgust on their faces, just steely determination.

"We're ready for you to detain the prisoner," Anias said, yanking Castiel forward so hard he nearly stumbled.

"Anias," Castiel tried. "What are you doing?"

"Please, Castiel," Anias said with disdain. "You know well enough what happens to wicked, fallen angels. They go to the darkest depths of Hell."

Castiel's heart froze in his chest and his legs nearly gave out as the two demons took him, one on each arm. "No. No please. Brother, you can't—"

"You are not my brother, Castiel," Anias said with such surety, that Castiel choked. "You are no longer a brother of Heaven at all. You are only Fallen. Officially, you are dead."

"Don't do this," Castiel pleaded one last time.

But no sympathy came. The demons yanked him forward again and Castiel was forced to obey, dragged closer and closer to the rift, until they entered the Gate of Hell and Castiel knew that once that happened, there was no turning back.

As Anias had said, he was as good as dead.