Sasuke's soul mark is frozen at birth, (stuck at thirteen months, twenty-seven days, twelve hours, and thirty-two seconds). This usually means that the soulmate is dead.
But then he misses a branch in the trees, one he was sure would be there (he hasn't missed a branch since he learned to augment his muscles with chakra), face plants a tree trunk and wakes up with a bloody nose, a headache, and a timer that starts counting.
He doesn't really know how his soulmate came back from the dead, or what it really means until he makes it back to Konoha, and Konoha is very much not there. Which means he's more than half a century in the past.
He bandages his wrist because every time he looks at the numbers his body lights up with stress and his sharingan threatens to come to life. The townspeople are not exactly unkind to Uchihas, but definitely on edge around him, which in turn makes Sasuke way more tense than he already is. The bandages stay on, and Sasuke pretends like he isn't keeping a mental track on the day he estimates to be the day he meets his soulmate.
Sasuke doesn't plan a lot of things in his life. A lot of his choices are spur of the moment decisions that he sticks through with because… well he's not entirely sure. Sakura calls it stubborn idiocy, Naruto calls it endless dumbassery (pot meet kettle), and Kakashi calls it Uchiha Pride. Sasuke himself would lean towards Uchiha Pride, entirely because the only Uchihas he's interacted with since he was seven are almost exactly like him, in the sense that every one of their plans blew up in their faces, took at least twelve casualties in the blast, and they're still convinced that their way is the right way. If you take about fifteen seconds to think about it, (which is fourteen more seconds than any of them took) it's clearly not. No other clan seems to have this problem, and if Sasuke were a lesser man he would envy them.
Without a goal in mind (because as much as he thinks of his old team, Sasuke has no real desire to go back to his time, and yeah, a lack of running water sucks but Sasuke lived in Sound for two years, he's used to roughing it) Sasuke just kind of… drifts. He travels all around the continent, markedly different without the hidden villages, and wonders if they even miss him back home.
They probably don't. Even he knows he's a massive ass.
The sentimental drivel isn't something that Sasuke enjoys thinking about, or something that he thinks about often, and it's usually only triggered when he sees a blinding color of orange, or sees a passing Hatake (Kakashi is most definitely the outlier in the cases he's seen) or when he breaks a bone doing something massively stupid.
(This association, he knows, would cause Sakura to actually fling him across Fire Country, but she's probably the only person who would btoher to fix any of his wounds. Konoha isn't exactly kind to traitors, and for a good reason. Even after everything with Madara, he's still regarded with intense suspicion, understandably so of course. Sasuke knows how the public views him- viewed him, and he didn't exactly go out of his way to fix it.)
This time, the sentimental drivel is triggered by a boy. A teen more accurately, with long blonde hair and a bit of a hole in his chest, (which morbidly reminds him of Naruto) probably caused by a spear of some sort. From the mass of bodies and the strong scent of blood and fire in the air, Sasuke assumes there was some sort of clan vs clan battle going on. Sasuke doesn't really care who the combatants were, instead debating on whether or not he should bandage up the wound and see if the kid makes it through the night. From the heavy breathing, he would guess that the kid would maybe make it through the night with some mediocre medical attention and well…
Sasuke has nothing against killing children. It may leave a bad taste in his mouth and make him hate himself just a little bit more, but he's done it before, and if the kid turns out to be a threat he can quite easily take care of it. He has two overpowered dojutsus and about as many weapons on him as Tenten carries to lunch (which, with the weapon mistress, is enough to fill at least three sealing scrolls) taking on a heavily injured teenager will be no problem.
The fire crackles and the seals that he put up on instinct pulses around the perimeter he set up. This seal in particular is a favorite of Orochimaru's and over the years of annoying bandits thinking they can get the drop on him (someone renowned around the five nations for engaging in hand to hand combat with an actual goddess) getting their dumbasses fried, Sasuke has grown quite fond of it as well.
He had placed the kid on the ground underneath a massive tree, and it's morning when the crinkling of the grass beneath the blonde notifies Sasuke that he's woken up, and knows that there's someone near him. Given Sasuke's automatic reaction to waking up in a place he doesn't remember falling asleep in is to summon a fireball and try to burn everything to the ground (Karin has and never will let Sasuke live that down), he figures the kid is doing all right in terms of panic and general paranoia.
Sasuke stokes the dying fire and the kid twitches. He wonders idly if the kid thinks Sasuke is actually fooled into thinking that he's asleep.
And it goes like that for a good half hour. Everything Sasuke does causes a visible reaction in the kid and it occurs to him (by the truly horrific fake sleeping) that the kid might be a lot younger than he originally suspected. He stares hard at the blonde and guesses that the kid could probably pass as a tall ten year old if you really squinted.
"Are you going to stop pretending to be asleep?" He says, and it comes out gruffer than he intended (entirely because Sasuke has not talked in almost a week now), but at this point he doubts that the boy would be any less tense if it came out any smoother.
With what Sasuke thinks is supposed to be a nervous chuckle (it sounds more like a series of deliberate wheezes) the kid sits up gingerly, leaning himself against the tree trunk behind him. "You caught me." He says, and through the fire light he can see a set of nervous forest green eyes and a bloodied smile. There's a striking resemblance in the jaw and slant of his eyes to three of the faces on the Hokage mountain and Sasuke barely suppresses a groan. A fucking Senju, or more hopefully, some weird Yamanaka. Getting him back to wherever he came from just became a million times trickier.
He scowls and glares at the fire, before looking back up at the nervously diminishing smile and sighing. "I don't suppose you have a way to get back to your clan without all of them trying to skewer me?" He huffs out, watching the probably-Senju-but-hopefully-Yamanaka's face for a reaction.
The kid's face is carefully blank as he answers, "why do you need to bring me back? You could just leave me."
Sasuke rolls his eyes at the not-answer and does not mention that the thought of leaving the kid hadn't even occurred to him after he had bandaged the errant, probably Senju, up. "Whatever." He says finally and kicks some dirt over the fire to put it out. It'll take both Tobirama and Hashirama combined to subdue him and Sasuke doesn't plan on being there that long for that to happen. With a huff he slap's the seals anchor and the chakra surrounding them dissipates. "Any chance you won't freak out if I pick you up and ask you to lead the way?"
When he doesn't get an answer he turns a dispassionate stare to the kid and drops down to eye level. "Look," green eyes stare pointedly over Sasuke's shoulder, "nothing is stopping me from leaving you here to die, but the only thing stopping me from carrying you back to whatever the hell clan you come from is you."
And it's true, the only thing he has to loose is his life, and Sasuke completed his life long goal of revenge a long time ago (to the sure surprise of his younger self; the only thing he feels now is regret and the bone deep loneliness that comes with knowing that you're the last, even if it is for the better).
The kid seems to mull it through for a minute before shrugging and pointing west. "Just drop me off about seven miles thataway and get away quick. My clansmen should be able to sense both me and you, and they won't be pleased to have an Uchiha so near clan grounds but…" he stares west, absently messing with the blonde strands, "I promised I would come home." The blonde clears his throat and blinks rapidly. "More importantly," he continues, turning to stare at Sasuke's empty sleeve, "how are you going to carry me?"
Sasuke huffs and hauls the kid onto his shoulder with the ease of someone who's been missing a limb for quite a while and one pained wince from the kid.
He heads west.
In theory, he was supposed to drop the kid off and run away immediately.
In practice it is fairly difficult to put down roughly one hundred sixteen pounds of injured muscle without damaging anything else. Upon getting the kid on the floor he realizes that the kid is starting to bleed out heavily, likely due to all the jostling of his wounds. The boy's already slipping out of consciousness, and Sasuke's not sure how far away the Senju clan is, he can't sense it from here (but, well, Sasuke's range is just short of pitiful), and therefore can't accurately judge how long it will take them to get here.
With an aggravated sigh (and he knows that Suigetsu is laughing his ass off somewhere) Sasuke kneels down to assess just how long the kid has before he bleeds out and dies on the Senju's front porch. Sasuke can't tell what's worse, staying to keep the kid alive and then be questioned as to why he stayed and what his dastardly Uchiha plans are, or leaving, the kid dying, and the Senju take it as a threat and start to actively hunt him and his clansmen of this period down.
It takes a few seconds of thought to realize that it's better if they don't try to hunt him down for a perceived threat, and decides that he can try bandaging some more and if it comes down to it he can use some bastardized medical ninjutsu to seal it up. The medical ninjutsu he knows is for small lesions only but Sasuke's fairly certain he can heal up a decent sized puncture wound.
Maybe.
He sinks down to one knee and prepares himself to run if anything pops into his small range. He pops out a sealing scroll and forces a blood pill down the kid's throat before applying more dressings and pressure, hoping that someone more qualified than him takes over soon.
He hisses quietly when three signatures pop up in his radar. One, very big, the other more like your average kage, and the last is barely above a civilian.
He hears a gasp, something almost like a snort, and "Hashirama-sama, your timer!" From behind him and Sasuke tenses at the words, (Hashirama fucking Senju, his mind screeches) and pulls at least twelve shunshins in the opposite direction and runs, possibly harder than he ever has in his entire life.
Once he's halfway into the heart of Rock and panting like a bitch in heat, he rips off the bandages on his soulmark and the timer reads a damning row of zeros.
Sasuke kicks a boulder and breaks his fucking foot.