It's dark when Dean wakes. His hand is already on the knife under his pillow when he hears a familiar voice.
"Fuck, Cas. You ever gonna knock like a normal person?"
"I am not a person."
"No, you really aren't." Dean pulls himself up, looks over at Sam, somehow still asleep, in the other bed. "Sammy," he says. "Wake up. We got company."
"Sam will not wake up," Castiel says. "You're the one I need. Get dressed."
Dean remembers to bend his knees right before Cas hits him in the forehead, and then he's in a motel parking lot in the middle of the night. "You know I could'a just used the door."
"We are not where you were."
"Duh." Dean looks around. It's vaguely familiar, but he can't put his finger on it. "Time travel, again. At this point I'm not even surprised."
"The year is 1999," Cas says. "You and your brother are in room number ten. I need you to correct the timeline, or the world will end, Dean. Nothing else can stop it."
"I get it. I'm here to make sure the Y2K bug nukes the internet, right?"
"That will not save the world."
"No kidding. Life ain't worth living if I can't have internet porn."
"This is important."
"Then why don't you tell me what the fuck I'm doing here."
"You made a choice in that room in 1999. One that will have dire consequences in the future. You're here to change that."
Dean gets a sick feeling in the pit of his stomach. The blue neon sign on the roadside is familiar, and the way it turns the curtains in the motel windows green.
A flash of memory hits him, the inside of a room, wood-panelled walls and yellow curtains. Sam, all of sixteen years old, angry cos Dad ditched them again, taking it out on Dean, shoving him against the door, using the height he gained during his last growth spurt and then—
"Is this a joke?" Dean's voice cracks. "If this is a joke it ain't fucking funny, Cas."
"I'm not laughing. I'm deathly serious. What happens here tonight—rather, what didn't happen. It must happen, Dean."
"Sam kissed me," Dean hisses, quiet, like someone could hear. "You want that to go away? You should've brought Sam here."
"It's not the choice Sam made that needs to be corrected, Dean."
"What?" Dean's been through this before. Racking his brain for something, anything he could have done different to make it not happen. "What do I have to do? I swear to god, Cas. If I did something to encourage him, I've spent the last ten years trying to figure it out. So just tell me what it is so I can fix it."
"You didn't encourage him. Dean, that's what you need to change. You pushed him away. It can't happen like that again or we're all lost."
"I gotta—?" Dean stares at Cas, waiting for the punchline, waiting for any of this to make sense. "What the fuck are you talking about? I gotta let him kiss me? I gotta let my baby brother, my own flesh and blood, kiss me? How the fuck is that gonna fix anything? Don't you guys have, like, rules about that stuff?"
"Humans have rules, Dean. Some of them make sense. In this instance, they do not. And in fact, letting your brother kiss you—and more—will save the world."
Dean gapes. "And more? How, exactly, is...I dunno, banging my kid brother...gonna save the world?"
"We're wasting time," Cas says. "Your younger self will exit the room in moments, and you must convince him."
Dean blinks, and Castiel is gone. Dean looks toward Room 10, and hears the key in the lock, sees the door crack open.
He ducks behind the vending machine he already knows is his destination.
"Look," Dean says, his younger self pinned to the asphalt beneath him. "Last year you put on a pair of pink satin panties and you loved it, and I swear to god that is the last time I'm gonna remind myself of that. This time travel thing is getting old."
Finally, the kid beneath him stops struggling. "How do you know that?"
"Because I'm you. Jesus, when was I ever this stupid? Can I let you up now? You gonna run?"
Dean—the smaller, slighter one—shakes his head. Dean releases him, and the kid stands, brushes himself off. "You're really from the future? Why, what's happened? Is Sammy in danger?"
Dean clings to that, because Sam is in danger. So is the rest of the world, if what Cas said is true, but Dean—both of them—can only focus on that one truth. "Yeah, he is. We all are, but if you wanna make sure Sam lives to see thirty, you gotta do something you're not gonna like, because I was you, and I remember, and it never crossed my mind—"
That's a lie. Dean's lying to himself, the version of himself where it's still fresh in his mind, and he can't lie now, not when this baby-faced kid has to believe him.
"Okay, it did. Dammit. Fuck. Look, we both know how we feel about him." He doesn't need to define who, they both know it. "But we'd never, right? He's our kid brother. We're supposed to protect him."
Dean's younger self takes a step back. "What did you do? What will I do? Just fucking tell me and I won't, okay, I won't lay a goddamn hand on him I won't—"
"You got to," Dean says. "The problem is, you didn't. He kissed you—will kiss you. Tonight. When you go back in that room, he's gonna kiss you. I pushed him away, because I thought it was the right thing to do. But it turns out it wasn't. And me, you, Sam, everyone in the goddamn world, we all die. So you can't."
The parking lot is still dark. The neon sign flickers. There's a bang from the other side of the door of Room 10, and Dean hopes he did what he needed to do to convince his younger self.
"Are we good?"
Castiel is silent for long moments, as though he's waiting for something.
He is waiting for something. He's waiting for Dean to kiss his brother back.
Finally, Cas nods. "We are good."
Relief floods Dean, and it hits him for the first time that as impossible as Cas's story sounded, he believed it. "Good." He's probably kissing Sam right now. It's what he would have done, if he'd had permission, if he hadn't thought that somehow, it wouldn't fuck Sam up.
Though he's not sure about that, if he's honest with himself. He might have saved the world, but what about Sam?
"Can we go? Before this gets awkward?"
Castiel touches his fingertips to Dean's forehead, and he's yanked away from the motel parking lot.
The room is still dark when Dean wakes, but there's a glow behind the thin motel curtains that means it's morning.
He groans, stretches out his arms. Ruffles Sam's hair where his head lies on the pillow right beside Dean's own. "Rise and shine, Sammy."
Sam makes a non-committal noise and pulls the blankets further up around his face.
"You'll never believe the dream I had."
Sam grunts. "Don't need to hear about your sex dreams, Dean."
"There was an apocalypse...I think?"
Sam's face appears. "Zombies, or, like, biblical?"
Dean rolls onto his side, just so he can shrug. "I dunno. There was this weird guy in a trenchcoat. And I was talking to myself—like, face to face, you know?"
"Is this where it gets kinky?"
Dean smirks. "I wish. Sadly, I woke up. But hey, you wanna make it up to me?" He rolls onto his back, peels the blankets away to bare himself to his brother. "You could cure my disappointment in no time."
Sam rolls toward him, starts to move down the bed. "We gotta be at the morgue at nine."
"We'll be there," Dean says, tangling his fingers in Sam's hair as his eyes roll back in his head.
wincest saves the world, I don't make the rules