Note: This is EMS Sasuke. He gets sucked into another time/dimension right after he hears Hashirama's story, but he hasn't joined the war yet.
The world spun. Bile rose up in Sasuke's throat. Words distorted in the air, space warping and twisting. Jugo and Suigetsu looked on in utter befuddlement. Sasuke's lips weakly parted to berate them, but no words came out.
Suddenly, he became hyperaware. Every tissue, every cell, every atom in his body, it felt like how Onoki's Atomic Dismantling would. Is this death? A genjutsu? If his body was intact, then the sensation of his limbs tearing was an illusion. Sasuke's only thought was the overwhelming desire for this feeling to stop.
And it did. For a split second, Sasuke heard the sound of his blood flowing within his veins. The silence was crippling. A second later, he was falling through the sky. Reflexively, he spread his arms out to slow his fall. The air he inhaled was sharp and cold. He noted with increasing annoyance that his clothes had vanished. He would die naked. Not that it was shameful; Sasuke had a killer body. Literally.
Luckily, Sasuke vaguely made out the shape of a large lake in a forest, steering towards it. His only hope was that it was deep enough for him to survive. There was the question of how he had ended up careening through the sky, seemingly teleporting from the borders of Konoha in the peak of autumn to an unknown place in the midst of a brilliant summer. That would be figured out later.
Sasuke's collision with the water was smooth, in which he phased through it and waded through the clear water to the edge, propping himself up on the grass. The first thing he did was analyse his surroundings. The scenery was picturesque, but he was not here to admire it. Sasuke closed his eyes, sensing chakra around him. Animals and other woodland critters, as expected, but a kilometre away, there was a cluster of civilians.
The cogs in his brain twisted and turned, trying to solve the mystery of where he was and how he got here. The only plausible explanation he had so far was that this was a space-time freak accident. Other than that, his situation was inexplicable. Thus, Sasuke vowed to piece the puzzle as he progressed in this unknown world.
With a grunt, Sasuke stood and began trekking to the small town. Without his clothes, his skin was exposed to the hot air of the forest. He promised himself to pilfer clothing as soon as he could.
Throughout walking, he dared not think of his predicament. Sasuke focused himself on his destination, watching where he stepped. Otherwise, traps and sharp objects were unpleasant to step on. He would not use chakra in the event that somebody would sense him. Instead, he suppressed it.
As the town neared, Sasuke genjutsu-ed civilians into ignoring him, using minimal chakra. He pushed away his discomfort at roaming around in a public place sans clothes. Eager for clothing, Sasuke began sprinting towards the town, easily evading the few shinobi, probably a Genin team on a C-rank. He noted with caution that their hitai-ate was Ame.
Sasuke strutted into a store and grabbed civilian clothing that he estimated were his size. He picked loose black pants, an open black jacket that he zipped up, shinobi sandals and black fingerless gloves, because they looked cool. It was presumably the most flexible, comfortable and unnoticeable piece of clothing in the store.
He eyed a newspaper, eyes widening at the date and headline.
The Yellow Flash!
Namikaze Minato of Konoha, a seemingly ordinary Jounin, decimates 100 Iwagakure ninja in a second. Iwa and Kumo are hard-pressed to keep up with this beast!
This was not a genjutsu; his genjutsu abilities were too strong for such a genjutsu to seem so real. If this was the Infinite Tsukuyomi, Sasuke knew it would work exactly like this. If he could change things, and save his clan, this would be the perfect time period.
Yet, there would be no breaking it. No matter what he did, if this was the Tsukuyomi, Sasuke was stuck. He never thought of the Infinite Tsukuyomi as a vile outcome, having considered it numerous times. If it was, he'd take his chances and live blissfully with his clan.
Sasuke questioned many things, but he knew that answers to those questions were nigh impossible. He dropped the genjutsu, sneakily stole a map of the Elemental Nations along with a loaf of bread and settled under the branches of an oak tree. After skimming through the map, he deemed it useless and returned it.
He pondered what to do. Sasuke was in the past, during the Third Shinobi War, and he spent sleepless nights studying the history of it back in the Academy days. If you asked him to, Sasuke could detail the textbooks, word for word. He knew that disaster was imminent. In a couple of decades, legends such as Akasuna no Sasori, Hoshigaki Kisame or Hidan would terrorise the world. At present, they were significantly weaker, if not a snivelling brat.
Only a fool would throw away the opportunity. Sasuke took his presence in this time to say that things weren't meant to stay the same. His clan was breathing. Madara was weakened. Tobi was presumably an integrated Uchiha, or even a child, whoever he was. Tobi's demise alone would change the world for better. Sasuke assigned himself a mission: find Tobi, and kill him.
To do that, he'd need to go back to Konoha.
During times of war, any and every site was a battleground, or, as Sasuke called it, a dumping ground for the dead. Sasuke was an adequate sensor at best, but even he could sense the masses of chakra pooling in certain areas. He had a Kage-level chakra signature, hard to suppress towards excellent sensors, so it would be best to travel along the battlegrounds to blend in.
Sasuke concealed his smirk as he traipsed through the forest, effortlessly evading the hidden traps. He paused. A kunai embedded itself into a tree trunk. A dozen more followed. A Kumo ninja emerged from the bushes, staring at Sasuke threateningly. Sasuke inwardly scoffed. The shinobi was decidedly a typical Jounin. The Kumo ninja couldn't even blink before Sasuke whacked him over the head, successfully knocking him out.
With a silent grunt, he resumed walking. He formulated a fake backstory for himself in his head. It wouldn't be hard. To quote Danzo's words, Sarutobi was a fool.
As he neared Konoha, tons of chakra signatures dotted the borders. Kumo and Iwa Chunin and Jounin were engaged in combat with Konoha shinobi. As a result, they weren't as aware of their surroundings as they should be. Sasuke's face remained indifferent as he sped through the trees, maneuvering through the foliage.
A three-pronged kunai barely missed his left ear. Sasuke backflipped off the tree branch, meeting eyes with his new opponent. Had he been an ordinary person, he would be bound, interrogated and possibly killed. It was a good thing he was not, for Namikaze Minato glared at him with utmost ferocity.
Three less-than-intimidating faces popped out from the bushes, watching with barely concealed eagerness. Sasuke's eyes imperceptibly widened at a mask-wearing face; it was a young Kakashi. Due to his veiled shock, Minato, who resembled Naruto so much that it hurt, held a kunai to his neck, standing behind him. Sasuke dispersed into tiny white snakes, reappearing behind Minato, not to the latter's surprise.
He had no intention to kill Minato. Namikaze was too influential of a figure to kill, his death would prevent Konoha's victory, too much would change with his death, not for the better. Sasuke pushed the image of a blond boy with whiskers away. He was also not stupid; facing Minato Namikaze would not end well for him. Minato would not kill him unless he provoked him.
When Minato and his Chunin turned their heads to face him, Sasuke's three-tomoe Sharingan was on full display, gleaming brightly. The thought would never occur to even the wariest shinobi that an Uchiha was not from Konoha. Sasuke wordlessly continued on his path, not paying them any attention.
"Is he mute or something?" He heard the black-haired, black-eyed boy whisper. He looked suspiciously like an Uchiha, albeit his attitude couldn't be further off.
"What's your name, Uchiha-san?" This came from the brown-haired girl. She emerged from the bushes, brushing off leaves and dust, smiling at him weakly. Minato, Kakashi and the black-haired boy, stared at him awkwardly, expecting an answer.
"Sasuke," He quipped. Using his real name would be seen as a dumb move, but Sasuke's name was the first thing that his late parents gave him. He refused to give it up. Sasuke made to perform a Shunshin, but the black-haired boy sauntered towards him, looking up at him hopefully.
"My name's Uchiha Obito, and I'm gonna be Hokage! After I get my Sharingan. Ano sa, I've never seen you before," Obito grinned obnoxiously. Sasuke blinked in reply. So he was an Uchiha after all: a mind-numbingly enthusiastic one.
The way he was looking at him, Obito was begging for Sasuke to give him advice to help him activate his Sharingan. "If you want to awaken your Sharingan," Sasuke paused for dramatic effect, "Work hard, and think about your goal." Everybody present was exasperated at the statement. He didn't let them dwell on it any longer, body flickering to the Konoha borders.
Security around the borders were lax, and not stupidly so. Shinobi were engaged in battle around the borders, and even Sasuke got caught twice. The two exhausted guards didn't pay any extra attention to him when he flashed his Sharingan, though they should have, it was good for him that they didn't.
"Idiots." He thought as he strutted through Konoha to the Hokage tower where the biggest idiot of all resided. Nobody even spared him a second glance. All he needed to do to infiltrate Konoha was reveal the Sharingan. Perhaps it was because he looked like the epitome of Uchiha: dark hair, dark eyes, aristocratic features, and mysterious.
"I need to speak to Hokage-sama," he spoke towards the receptionist, who continued to fill out paperwork. She irritatedly glanced up at him.
"Hokage-sama is busy right now." Sasuke didn't waste his time on her, marching up to the Hokage's office. The receptionist didn't care as much as she was supposed to. Luckily for Sasuke, Hiruzen was alone and scrawling out paperwork.
"Hokage-sama," Having to respect this incompetent fool physically hurt. Hiruzen glanced up, silently beckoning for Sasuke to say whatever he wanted to say.
Sasuke approached him, plopping himself down in the velvet chair in front of the Hokage's. Hiruzen, apparently getting the memo that this was urgent, faced Sasuke with a stern look. Hiruzen signalled for the ANBU to leave, activating privacy seals. "I am from the future." Hiruzen gaped, completely disbelieving, but he remained quiet. Sasuke inwardly smirked as he started monologuing.
Let the deception begin.