Maybe that was the whole point of why the Apocalypse was so built into, why everyone was always so terrified. It’s not because Earth would somehow have a greater dying than the Great Dying – no. It’s because, angels, well—
He remembers energy flowing through him, death upon death, out of control, but so so in tune with the vitriol and sense of betrayal when all he wanted was to –
Naomi makes him kill his friends. He falters, like he did with Dean. But the connection doesn’t break. She tells him in Enochian to not worry. This species will lead to humanity, the great prophecy. Cas never gave a fuck about directional evolution. He just remembers caring about his friends. Maybe their species survives. But they didn’t.
It has been 252 million years. There is a forgotten grief inside Cas that threatens to swallow him whole. He had been real before. They were significant; they mattered. And Cas was made to forget. Does he even know what he would be if he hadn’t been made to forget?
How much of who he is is just – gone?
He loved them. He doesn’t even – he doesn’t even remember – he loved them.

The light overwhelms, familiar though it may be.
 
Fingers soft on his forehead and—
 
(Being eight.) (Collapsing in the school gym.) (His body is a war zone.) (Big brother shaped hands with an old rag) (soaked with cold sink water.) (They don’t own a thermometer.) (There’s nothing that could heal Sam of what he is and what he’ll be.)
 
(Then there is the darkness.) (Then there is always the darkness.) 
 
(Sam has been falling into it his entire life.)

Now Sam thinks about it, he can see that metaphorically speaking, the two of them have a history in this area. That’s the reason he was so ready to accede to Castiel’s plans today. Looking back through the strange sharp filter that overlays those memories of the Sam that wasn’t him, he can see Castiel’s hand plunged wrist-deep, rib-deep, inside his torso. He can feel (has felt, has thought about in that doesn’t-count moment before he comes) the brush of Castiel’s fingers against his soul. He can remember, too, Cas with a long syringe in his hand, a needle in Sam’s neck, draining the remnants of Gadreel. That had hurt, and it had been dangerous, and Sam hadn’t wanted him to stop.
Cas isn’t misreading, then. But what he’s suggesting is different, even for all the ways it isn’t.
“Are you sure you’re okay with this, Cas? This isn’t, um - for people, this is. I want it, but. This isn’t the same as what we’ve done.”
“No,” says Cas, “I know. I’m sure. I want to do this.”
Sam waits for Cas to add, “for you”. But he doesn’t. So Castiel does get something out of this, the strange dynamic that has opened up between them - the ritual of Cas pushing into Sam, scraping away at his insides. It’s hard to know what that might be without answering other questions about the way Cas thinks of him. What is Sam to him, now?

It feels a lot like laziness; or being kinder to himself, exhaustion. There is so much careful work required in the construction of a relationship. He’s not sure he has the energy to figure out how to fit himself to another person, how to fit that person into the unshapely mess of his life. It’s different than a one-night stand might be. That would be okay. It’s just sex. It’s just bodies. A relationship requires a different kind of nakedness and Sam’s not sure he has the stomach for that anymore.

Since the Cage, he's always known he can never trust his mind completely, never be fully certain what he sees and hears. But his body - the pain of his scar when he presses down on it for comfort, the movements seared into his muscles from decades of fighting, his ability to fight through the pain when he's knocked down and get back up - he's trusted that, even trusted what's in his blood enough to hate it. It's kept him tethered almost as much as Dean has. Now he can't even trust his own ability to get out of bed in the morning. 
He hasn't lost hope yet, he really hasn't - it's in Sam's nature to believe in the impossible, he still hasn’t learned his lesson - but it's taking more and more energy to convince himself that things will turn out okay, and energy just isn't something he can spare much of right now.

A voice taunts him in the back of his mind as he grimaces and pulls himself up with the sink, catching another glimpse of the stranger in the mirror. Sam Winchester, always running away. His brain doesn't supply the helpful nuance of whose voice his subconscious is mocking him with, but it doesn't matter if it's Dean's, Lucifer's, his dad's, his own. 
He can't run away this time, not when his body is the thing that he wants to escape.

“Sam,” Castiel starts slowly, and Sam doesn’t jump this time, for which Cas is grateful. Sam looks at him, questioning when Castiel doesn’t continue for a few moments, and he steels himself. “Have you been seeing Lucifer lately?”
Sam’s body goes rigid and his eyes shutter, the mug settling on the table with a muted clatter as coffee spills from the edges; he doesn’t let go of it even as the scalding liquid splashes on his hands.
“No,” he grits out after a second.
And Castiel believes him, he does. But-- he reaches out and peels Sam’s fingers from around the hot mug, and holds him in his hands. His hands are pink, and the fingers are a deep red. The new scratches are already scabbed over, covering older scratches and scars.
“Does this help?” Castiel asks quietly. Sam doesn’t answer.
For the first time since healing the damage from the Trials, Cas heals Sam again. Letting the stolen grace burn through him and wash over Sam, not only healing his hands, but also easing some of the tension in his shoulders.
Sam still flinches hard before snatching his hands away. He starts rubbing at his palm furiously, biting at his lip.
Castiel’s heart aches.
“I’m sorry,” Sam starts, “I just--”
“It’s alright,” Castiel says. He can understand how an angel's grace could be disorienting and frightening after being possessed by one. He also understands the appeal of pain, the distraction it provides. The faux relief.
There is something indecipherable in Sam’s eyes as he stares at Cas, something small and uncertain. Cas wishes he had his own graces, that he was at full power.
He’d never felt helpless before he met the Winchesters. After that, helpless seems to be the only thing he feels.
A crack splits Sam’s voice through as he speaks, “Are you- are you real?”

“Sam,” he says, though he’s not trying to get away.
“Look, I’m trying to prove a point,” Sam says, sighing. “You taste—”
“Don't say my blood tastes good, don’t you dare—”
“No, I was gonna say human.”
“What?”
“If you weren’t— If you weren’t one hundred percent cured, I’d be able to tell, okay?”
Cas looks at him for a moment, not knowing what to do. Then he does try to get away, but Sam holds the blade against his throat again.
He bites back a moan, managing to replace it by saying, “Sam, please.”
“Listen to me. If you weren’t one hundred percent cured, I’d know. And I wouldn’t let this blade anywhere near you. And I think… I get it, alright? And you need to listen to me when I say there’s nothing bad left in there,” Sam says, putting his palm on his chest.
Right then, Cas almost says something about how he tried but couldn’t leave his body because of the tattoo in his chest. It worked both ways, as it turned out: no evil gets in, no evil gets out. Sam likes to pretend Cas wasn’t himself, but deep down, they both know the truth. He wasn’t possessed; it was him, trapped inside his body, chained to his unholy mission. Him, alone. Him, a God.

It is all so very unreal and messy. He’s just standing in the room when Sam enters, unperturbed in the daylight. Sam's head is buzzing so loudly that he’s not sure he can fully take in everything. His brain flashes a sensory memory of Lucifer owning him, and it’s louder than Cas’s voice could ever be. He’s tuned in just enough to see how nerve-racked Cas is.
“I don’t care that you’re a virgin,” Sam says. Cas nods, fiddles with his hands. It’s a bit unexpected, to be honest. Not that Cas is a virgin -- that makes sense, though Sam is envious he could live that long and not be forced to have sex at some point, but he guesses that’s what having angelic powers allows you. It’s just unexpected that Cas would care. Did he think Sam would judge him?
“I am trying to assess how compatible we would be,” Cas says. Sam worries his lip. It makes him feel a bit uncomfortable that Cas immediately jumped to sex like this. He gets it -- he’s not judging Cas for thinking through the unknowns methodically like this. It reminds him of how he had once dreamt of talking to Brady before--
But it’s just that, well. Sam hasn’t had sex since-- Sex isn’t what it used to be. And he doesn’t know if he can be compatible with anyone besides-- He doesn’t know.
“Okay,” Sam says. He feels like he’s roleplaying something that isn’t a ship wreckage. He racks his brain of what he used to like, but all he finds is shame. He thinks he used to like shame, too. He’s not sure if this is correlation or causation anymore. He wants to pretend it’s not inherent to who he is, but that seems somewhat laughable.

He lets Dean punch him, tie him to a chair, lets him get the anger out of the way. Sam tries to calm him with words and he makes his eyes extra big. But there's no use in pleading. He could run, of course. It would be easy.
Dean calls Castiel. It takes a while until he comes. He's surprised to see Sam bound up. Dean demands to know what's wrong with Sam and Sam expects Castiel to roll up his sleeves again. The thought isn't an unpleasant one.
Castiel touches Sam's forehead, and closes his eyes. "And?" Dean asks, just seconds later.
"He's perfectly healthy," Castiel says. "There's nothing wrong with him."
"What do you mean?" Dean's face falls. "Of course there's something wrong with him!"
Sam would really like to get some ice for his face now.
"Maybe something happened to him in the cage," Castiel suggests. "Maybe it's a side effect of suppressing trauma."
"That lets him lie to a goddess?" Dean scoffs. "No, you listen to me. I know Sam, and this isn't him!" Castiel follows his outstretched arm.
"I'm sorry, Dean," he says, "but this is your brother."