Cas has his grace, or whatever fragments were left, but he's still dying.

Because Dean is in the basement, but it isn't Dean.

This is the Dean that enjoys toying with broken people. This is the Dean that doesn't give a shit about the Impala. This is the Dean that tried to kill both Sam and Cas.

So Cas is upstairs. He's talking to Metatron.

Well, not talking, exactly. Metatron's been throwing a temper tantrum since he told them where Cas's grace was and they didn't set him free. And Cas hates Metatron.

So they're not talking.

Cas is pretty much just sitting in front of Metatron, gloating halfheartedly.

"Castiel?" Hannah says. Cas turns to face her.

"Hello."

"You've been sitting here for hours, Castiel. What is it that you're trying to accomplish?"

"Nothing," says Cas. "But it's better than being with Sam and Dean."

Hannah sighs, but seems to recognize that Cas isn't moving. She turns and leaves the prison.

Cas? You there?

It's Sam. He's praying. Cas immediately appears next to him. They'd been running an experiment of sorts on Dean, to see what would happen if he didn't kill.

He knows immediately something's wrong.

Tear streaks coat Sam's cheeks.

"Cas, he's dying," chokes out Sam.

"What?" asks Cas. "How do you know?"

"This." Sam shoves the enormous old book to Cas. It's open to the middle of the book and has a depiction of the blade on the page.

It says that after a certain amount of time without killing, nothing can be done for the bearer of the mark of Cain.

Cas reads it quickly. The hope extinguished from his eyes is actually visible.

"Nothing can save him?" Cas's voice comes out weak, fragile.

"I tried everything. I tried to cure him." Sam shows Cas the needle marks on his arm. "It didn't work. Nothing worked." Sam runs one hand through his messy hair. "Do you- do you think this is it?"

"No," Cas says loudly. The strength and steadiness in his voice even surprises him. "Believe me, Sam. I will find a way."

Cas is back upstairs, in front of Metatron.

"Metatron!" roars Cas. He steps forward and grabs Metatron, glaring at him. "How do I save Dean?"

Metatron laughs. "Oh, are we already there?" he asked delightedly. "You guys really need to deliver the Winchester Times up here."

"Do not play games with me, Metatron," warns Cas. He shakes him. "How do I save him?"

"What will you give me in return?" asks Metatron.

"I won't kill you!" shouts Cas.

"Have you considered going to counseling?" asks Metatron. "I hear that that's much more therapeutic than killing."

Cas deflates. "Fine," he says softly. "I'll let you go. Just tell me."

"Ooh, now we're getting somewhere!" says Metatron gleefully. "Let me out first."

"Save him."

"Okay, okay. All you have to do is give him a piece of grace. Not that much. The bare minimum." Metatron pauses, as if he's remembering something. "In fact, the amount of grace you have left would do the trick."

The immense relief that washes over Cas is inexplicable. "Thank you," he breathes. Cas unlocks the gate and cuts the straightjacket off of Metatron. "You can go."

"One more thing," says Metatron. He looks excited, smiling childishly at Cas. "It has to be willing. You can't just order an angel to give up a piece of their grace, even if it's a tiny piece. The angel has to genuinely care for the grace to work."

Then he's gone, leaving Cas to understand what he means.

Cas goes back to the bunker. Sam is lying on the couch, passed out. Beer bottles are littered around him. He's obviously drunk. Or as drunk as a Winchester can get, anyway.

Cas walks downstairs and into the dungeon. Dean is still chained up in every way imaginable, but it's doubtful he could leave even if he wasn't bound. Blood is dripping from his eyes, ears, mouth, and nose. His skin is peeling from his body. He's pale, but his eyes are still black. They've been black for days, since the mark started starving for blood.

The entire picture is breaking Cas. Dean is obviously in extreme agony, but he doesn't even seem like Dean anymore. He has a disgusted sneer on his face. When he sees Cas open the door, he looks up and grins humorlessly. "Oh, look at that. They're sending in the cavalry." His voice is weak and full of pain, but he doesn't back down.

When Cas steps closer, Dean spits a combination of bile, blood, and spit at him.

"I'm trying to help you, Dean," says Cas quietly.

Understand, Dean. Please.

Dean leans forward, and for a second, Cas thinks that he does understand.

"Fuck you," says Dean, pronouncing each syllable carefully.

Cas closes his eyes, trying to prevent tears from filling them. He pulls out an angel blade and places the tip at his throat, pulling a vial out of his pocket. Dean narrows his ink black eyes.

"What are you doing?" he asks.

"Saving you," says Cas. He's become somewhat numb, so he barely feels it as he draws the blade across his own throat. He does feel the tiny amount of grace drain out of him, though.

"No! Keep that shit away from me!" shouts Dean. He struggles in his chair as Cas walks over to him with a bleeding neck and a vial of grace. "Get away from me!"

Cas can feel the life draining out of him. They had never extracted the grace that had been killing him, and it's finishing the job now.

Cas forces Dean's mouth open and pours in the grace. Dean stops struggling, and his eyes droop shut.

"Dean?" asks Cas quietly.

Dean doesn't respond.

Cas's lips part slightly, and he sinks to the ground.

A trick. Metatron tricked him.

He shouldn't be surprised. He's not, really. It was his fault. It was a miniscule chance, and he held onto it too strongly.

Somewhere in an ocean of grief, something floats to the top.

He'd never told Dean that he needed him.

Why this sticks in the forefront of his mind, Cas has no idea. He doesn't care. He doubts he cares about anything.

"Cas?" Cas looks up. Green eyes are staring down at him.

"Dean." Cas stands up, a small smile lighting his face.

"Why'd you do it?" Dean asks. His voice is raw and tortured.

Cas doesn't answer. The last of the stolen grace has finally flickered out.

On Cas's last breath, he kisses Dean. It says everything Cas never got the chance to. He needs him, he loves him, he's sorry.

And then Cas collapses, and Dean is left with a body, a memory, and a pile of chains.