Hashirama is a lot more conscious when ambushed by a mirror snake; he is, however, occupied with trying to get it away from his clan members, and it's unfairly fast - 

When it eats him he appears crouching in the strange new area. The trees don't know him; the very ground feels odd, almost lifeless.

And there's an unconscious, wounded Uchiha five feet away.

He looks around, trying to get a hold - the area's almost barren, there's no wisps of nature chakra - 

But he doesn't feel any other humans for miles, and that Uchiha is close to death, and Hashirama wants peace even if Tajima and Butsuma won't allow it - 

He kneels, and slowly begins to heal the other boy.

Sasuke knows better than to tense when he wakes, or to change his breathing - he listens, tries to identify where he is and what's happening -

That isn't Karin's chakra healing him, and the healing feels... Almost unrefined. An inexperienced medic? Or someone without formal training?

And - he's not very good at sensing chakra, but the world around him feels quiet, and the person beside him very, very bright.

Hashirama finishes healing him then backs off. "I know you're awake," he says. "I'm not intending to fight you."

He opens his eyes, rolls into a crouch, looks at his healer -

And his face goes a bit blank.

Sasuke's good at recognizing faces.

That.

He's pretty sure that's teenaged Senju Hashirama.

His sharingan flickers to life.

He spreads his hands, palms visible and empty. "As I said, not trying to fight. We're both somewhere odd, I don't think it benefits us. Temporary ceasefires have happened before, we just need to each find our way back to our clans."

He flinches a little.

(He just killed the last of his clan.)

"You."

He shakes his head. "What year do you think it is?"

And looks around a bit, keeping the (maybe fake) Senju in his peripheral vision. The trees around them look more like the coral he saw in the Land of Water once, and there's tangles of seaweed-like grass that's oddly buoyant in the distance. Sasuke would think they were underwater, except what's around him's plainly air.

"...Uh."

He's not one of the people keeping records, and 'how many years has it been since the last Emperor died' is he thinks the usual referent but he's not sure on that. The twice he's been dragged into meeting a daimyo they just referred to the daimyo's reign.

"At least? One century?"

"For the Death Count - two hundred and seven. For me."

He drags a hand down his face. "It's been sixty four years since the shinobi village of Konoha was founded by the Uchiha and Senju clans. You're - either we both got kicked through the timeline, or you're a fake, or there's somehow multiple timelines..." Orochimaru might've talked about that, once.

He doesn't want to deal with this. He wants to curl up in a depressed ball and just. Not move. Itachi's dead and Sasuke's purpose feels like it's drained out of him entirely.

The Uchiha might be lying. Might be trying to trick Hashirama. But - he doesn't feel like it. He's not acting all that wary, not like an enemy would.

And it's a weird lie.

Still - 

"We founded a village?" Hashirama asks, a bit stunned. 

"Yeah." He shrugs. He doesn't know that much about the Land of Fire's history in that period, really - only thing he's read about from back then is the precursors to the Seven Swordsmen.

He relaxes from his crouch, sitting, and staring at his hands.

He really doesn't know how to process what happened with Itachi, and a timetraveling Founder isn't super helping that.

He sits too, at a loss for what else to do. He supposes he could explore the area, but... There's still an ingrained sense telling him not to turn his back on a strange Uchiha.

Still: "Are you alright?"

That's really none of his business.

(But Sasuke really, really isn't alright.)

He takes a deep breath and stands. "Come on. Let's figure out where we are."

Hashirama pauses, then nods, deciding to let the issue slide. It's not like the Uchiha has any reason to trust him...

"What's your name, by the way? I'm Hashirama."

"Sasuke," he says, looking everywhere but the other teen.

"Nice to meet you, Sasuke!" He joins the other in kind of performatively looking around. "So... Try to find civilization, or try and build a shelter on our own? I don't sense anyone other than you, but... Well, can't sense the plants, either."

Attempting to talk to people sounds like the last thing he wants to do ever.

It's probably the only way they're gonna get out of here, but... It's not like he has anything to do back to. Might as well camp in the wilderness. No Naruto to keep chasing him out here. Hopefully.

"Shelter," he says after an awkwardly long pause.

"Right!" Hashirama says cheerily, completely ignoring any social awkwardness. "We might want to set up so we can keep an eye on here but aren't right on it, in case other people show up!"

Sasuke nods, then jumps up into one of the taller coral-trees to try and get a look around. There's some high ground - a few places that might make good hiding spots already, but like caves there's a risk of inhabitants - that seaweed might make good lashing for a shelter, and there's a few broader leaves that can be worked together...

He hasn't noticed any insects yet, too, but they'll need to keep in mind keeping those away...

He turns his head, starts trying to identify where there's more clusters of life, or see if he can hear water. So far he hasn't seen any movement indicative of animal life...

Hashirama goes to identify good plants - he can if he touches something still get a sense of edibility; the seaweed should be fine for them to eat...

He's able to find a few animals in coral caves, too, brightly colored and mostly inclined to flee from him, though one unfairly fast insect-thing punches the air in front of him and sends him flying back several dozen feet, bruises and burns blooming across his skin and bones breaking.

...The First Hokage is a fucking idiot.

Sasuke gets behind the insect-thing, kills it with lightning, then runs to check on Hashirama, nervous about touching him because he so very much does not have medic training.

Hashirama, while he wouldn't really contest the 'idiot' part since, well, fair, does in fact have a healing factor. It's slower without natural chakra to draw on, but his burns are already fading and his bones are considering settling back into place.

He makes a very theatrical show of groaning.

"Are you safe to move?" Sasuke demands.

He cracks one eye open. "...Maybe?" he mutters, the words only sort of slurring.

Sasuke sighs and bends to carefully pick him up, carrying him away from Mystery Inhabited Caves and over to a small clearing at the base of some very-not-inhabited coral towers. "Stay here. I'll build the shelter."