And then, after a rousing speech, his true weakness is revealed. He's in love.

On borrowed grace from murdering his brothers and stealing their essence, Castiel had built an army. Sometimes his skin burned and sometimes white would flash so painfully in front of his eyes that he would be nearly incapacitated. The borrowed Grace within him, clawing at his organs and winding itself around his spinal cord, was burning him from the inside out, less like a bad fever and more like swallowing a cup of magma. He was dying, he knew that, and he accepted it, but he had to do one thing before he was pulled into nowhere, or wherever angels went when they died. He had to put heaven right again. He broke it, and he had to fix it.

He didn't see much of Dean throughout these few months, and what he did see of him was more than troubling. Dean had taken on the Mark. The dreadful curse that turned Cain to murder. The insatiable itch under his skin never being cleansed as he bathed in the blood of the innocent as well as the guilty.

Dean was headed down that road, and it was all Castiel could do to warn him.

With humanity.

Castiel had given his army up for Dean. Given everything that he had worked so hard to build. His army in exchange for the eldest Winchester's life. He couldn't be expected to kill the Righteous Man. That bright soul, blemished and marred with pain and the desire to kill. The only being he'd ever, truly, cared about.

Ah. So Gadreel bites the dust. And the Angel tablet - arguably the most powerful instrument in the history of the universe - is in pieces, and for what again?

Metatron spoke, not noticing the hatred and anger that swirled, barely concealed beneath Castiel's skin. It took all of his willpower to not stand and strangle the useless waste of existence that was God's scribe.

Oh, that's right, to save Dean Winchester. That was your goal, right? I mean, you draped yourself in the flag of heaven, but ultimately, it was all about saving one human, right?

Castiel would always save Dean. He knew that, and in that moment, Metatron knew. His enemy knew his one weakness, and if Castiel had had the sense to move, to leave, to search out the Winchesters in that moment, maybe he could've done something. But he sat there, shattered stone at his feet and glaring at the disgusting lout that had stolen his Grace and turned Heaven upside down.

Well, guess what. He's dead, too.

Castiel could feel his world fall apart. He could hear the blood rushing in his ears and from the moment that he looked at Metatron's smug face, he knew that it showed on his features. Dean was gone. Of course, Dean had been gone before, and it never lasted, but that didn't stop the irrational panic and hurt that flooded him.

And then Dean was a demon.

But it was after the righteous man was cleansed that everything really took a turn for the worst. That everything broke and slipped into the depths of the darkest days in Hell. He could've done more, he could've fixed it faster, but he didn't, he couldn't. It was only his fault that Dean went off the deep end. He hadn't been fast enough. He had been too caught up in fixing heaven when it had first begun and he'd had time.

Maybe you could fight the Mark for years. Maybe centuries, like Cain did. But you cannot fight it forever. And when you finally turn, and you will turn... Sam, and everyone you know, everyone you love... they could be long dead. Everyone except me. I'm the one who will have to watch you murder the world. So if there's even a small chance that we can save you, I won't let you walk out of this room.

He dropped his hand on the wrecked man's shoulder and pulled him back as he turned to walk away. He wouldn't let Dean leave, not when he could still be saved. Not when it was his fault. Not when he cared for Dean Winchester, loved him with the very core of his being.

Dean, I don't wanna have to hurt you.

I don't think that's gonna be a problem.

It was his fault that Dean turned, and he accepted the punishment.

His wrist was suddenly in Dean's iron grip, and was twisted. He heard a pop, felt a crunch, but it didn't matter. It didn't matter that between one blink and the next, Dean's fist connected with his jaw, rocking his head back.

Dean.

In an odd twist of disgusting irony, Castiel was on the receiving end of the fists, the hate, the anger. The Mark. He hadn't fought back, he had only tried to keep Dean from leaving, Dean couldn't leave. Dean had to be saved.

He was all that mattered.

Face bloodied and split, he'd been tossed to the floor, no better than garbage. Dean turned to leave and Castiel watched, managing to push himself up. His face was wet, swollen, throbbing, he could taste blood on his lips and his vision was unfocused. It didn't matter.

Dean, stop.

Dean had stopped. He'd stopped and wheeled around for a renewed assault. Worse than before, Castiel floundered and soon found himself on his back, staring up at Dean. Hard jade chips stared back as the man that wasn't the man he loved pulled out his angel blade and readied it. He had failed, he was going to die, just like that. His existence would be snuffed out by the blackened and twisted soul that had been so bright as he'd placed it back in his body. His last breath would be shared with the creature that shared a face with The Righteous Man.

Maybe he wouldn't have had it any other way.

Castiel coughed, thick red iron spurting over his lips as his hand made it's way to grab at Dean's wrist, the one holding his tie. He blinked and in one moment he wasn't looking at the thing The Mark had turned Dean into, but he was staring at the hunter, Dean Winchester. He was looking at the man he'd fought with, for, and about. The man he'd given everything for, and would give anything to, if only he'd ask. He was so hopelessly enamored with the man with the bright soul, he thought there was no other face he'd rather see right before he could no longer see anything.

Dean, please.

It was all he could muster. Whether he was begging for the sweet end of his constant torment, or his life to continue the torture, he wasn't sure. All he knew was that Dean was over him, around him, part of him, and he would never be able to get the scent of aftershave, whiskey, and car grease out of his memory. It had burned into him, and he was reminded every time Dean passed, but now it was thick and heavy with the iron tang of blood. It was Dean, but it wasn't. He had failed, once again, and he was losing Dean, as well as himself.

The blade arced through the air, glinting bright silver in the light as it dove down to lance through his heart. He was at war with himself, half of him screaming Yes, yes, please God, just do it. and the other half begging Dean just to kiss him first, just so he could know what it felt like to have the man he'd pined after love him too.

Neither of these things happened. Instead, with a dull thump that was mimicked by his unsteady heart, the tip of the blade made it's way into the book beside his head. He was still alive, he knew that by the breath in his lungs, but he was oh, so dead.

Next time, I won't miss.

But Dean hadn't missed. As Castiel watched his broad back disappear behind the wall, he felt worse than if he'd been run through, grace beaming through the room and black wings etching alongside his body. He had failed the only thing that mattered. That had ever mattered to him.

He had failed Dean.