I really wanted to write something for the AceSabo Week event currently ongoing on Tumblr (March 20-26), and I adored the soulmate / body swap theme of the 2016 anime movie Kimi no Na wa, so I thought why not combine both?

This story does not require you to have watched Kimi no Na wa, though there are some elements in the plotline which would factor as spoilers for the movie if you decide to watch it later, so be warned about that. But otherwise, on to the story, and as always I hope you like it!

Sabo slowly awakened to the gentle sensation of a breeze blowing against his face and the bobbing sway of a boat on the sea. The faint reddish glow of dawn stole past his closed eyelids, gradually brightening with every passing moment.

Had he fallen asleep above deck? It wouldn't be the first time he'd done so, Koala often liked to comment on his ability to fall asleep virtually anywhere at any time.

The bright glow of the rising sun finally became impossible to ignore. Sabo sighed, knowing that if he didn't get up soon, he would have Koala ragging on him again for sleeping out in the open where any passing ship might catch sight of his now rather infamous figure. Following the events at Dressrosa, he and the other members of the Revolutionary Army were sailing back to Baltigo on a modest-sized warship they had hijacked from Dressrosa's underground port. It would take them another week or so to arrive, and she'd have his head if any trouble happened in the meantime.

With that in mind, he reluctantly cracked open his eyes.

The sight that met his eyes threw any last vestiges of sleep from his mind as he bolted straight upright.

The small boat that he was lying on swayed rather dangerously in protest from the sudden movement. The wide expanse of sea greeted him from every direction, from a much closer angle than he had expected. It was most certainly not a warship. Far from it. It really couldn't be described as anything other than a dinghy, albeit a very sleek-looking modern-style one.

His first thought was that Koala had pulled a prank on him and deposited him on a lifeboat as revenge for the trouble he had caused her these past few days (or years, if one wanted to track back that far).

But if that was really the case, he would expect the large shadow of their ship to loom up ahead, pulling along the dinghy by a mooring rope. No matter how mad Koala was, she would never do something as reckless as throwing him overboard to fend for himself in the middle of the New World, especially after he had just eaten a Devil Fruit a mere few days ago.

But the warship was nowhere in sight, not even as a silhouette in the distance. There was absolutely nothing but open sea all around.

Something was definitely wrong here and Sabo didn't like not knowing what had happened.

By reflex he reached for where he usually kept his personal baby den den mushi as he warily scanned his surrounding for clues, hoping that he still had it to contact Koala at least. Instead of finding a pocket his fingers touched nothing by air, and it was only then that he realized that he was completely shirtless. With the powers of the Mera Mera no Mi automatically keeping him warm, it hadn't been an issue his mind had processed.

But it wasn't just that. He stared down at his bare forearms, tanner than his regular skin tone which burned all too easily. He frowned, flexing his fingers. The digits responded automatically to his directions, despite the overall wrongness. Years of training had made Sabo familiar with the structure of his body, the pull of muscles that allowed him to fight the way he was used to. The body he was currently in was broader around the shoulders, legs shorter and tightly muscled in a way that was different from Sabo's lanky and leaner form. More strength than speed, raw power rather than controlled Haki.

This wasn't his body, so the question now was whose was it and perhaps the bigger question was just how the heck had he ended up in this strange situation.

His eyes swept over the strange body, picking out features that could be filed away as clues. The black cargo shorts and sturdy boots were unremarkable, though the belt looped around his waist nagged at something in his memory. As he'd noted before, he wore no shirt, though there was the heavy sensation of an accessory around his neck. Some kind of necklace? His eyes shifted down towards it, his hand reaching up to inspect the item, but his gaze snagged on something else and Sabo felt his breath leave him in a sudden, sharp motion that left him dizzy.

After regaining his memories, he had dug up every news clipping and bounty poster of Ace that had could. He'd burned the image of him into his mind, that familiar yet unfamiliar grown-up Ace. But there was always one single feature that stood out the most, that brought a deep echoing ache to Sabo's heart. ASCE with the S crossed out, a clear tribute to his lost brother. To Sabo.

A tattoo that he now saw, unmistakably, on his arm.

He almost pitched overboard in his haste to reach the side to look into the water. Sea water rippled underneath the boat, making it almost impossible to see his reflection, but it was enough to see the hint of black hair, in sharp contrast to Sabo's own bright blond.

"It's a dream," he muttered, fingers clenching around the side of the boat so hard that the painted wood creaked. "It's got to be a dream."

Because the alternative was crazy, insane, impossible, and Sabo didn't want to let that bright burning hope grow if it meant that it was going to die all over again.

But… but if it really was true, if this really wasn't a dream…

Then…

Sabo yawned as he stepped out of the room he had bagged as his on their stolen warship, ambling down the hallways towards the mess.

"Morning," he mumbled as he entered the galley, making a beeline for the coffeemaker on the pantry counter. It took a few sips before he realized that the whole room was staring at him silently with strange intensity.

He glanced down at himself. He wasn't naked or anything, though he had foregone his coat and cravat in the privacy of the ship with just the few of them on-board. That was hardly enough to warrant the weird looks he was getting, was it?

Having determined that there was nothing on his person too out of the ordinary, he looked back up, arching an eyebrow. "What?"

"Oh good, Sabo-kun is normal again."

He blinked at Koala, confused at her words. "Huh?"

His old friend propped one hand against her waist, amusement warring with exasperation in her expression. "You were acting weirder than normal yesterday," she told him. "We thought you'd caught some weird bug back at Dressrosa or something."

Sabo wasn't sure that he really wanted to know, but he had to ask. "Erm… Weird like how?"

Koala raised her eyebrows at him. "You really don't remember? First you started out walking around the ship shirtless, and acted like you didn't know Hack and me, then you got all polite all of a sudden, and right after that you just started crying! It was crazy weird even by your standards, Sabo-kun."

Sabo could only gape back at her.

WHAT!?

It took him two more switches to finally believe that it wasn't just some weird dream. That as crazy as it sounded, he was actually swapping bodies with Ace for short periods of time.

Each time landed him on the same red motorboat smack in the middle of the ocean with no land in sight, the single-needle log pose on Ace's wrist clueing him in that he was in the Grand Line, at least. As Ace never bothered travelling with any kind of writing material, Sabo had no way of leaving messages. Ace, on the other hand, had no such difficulty on Sabo's side of things and Sabo returned to this body the next day to be greeted with a long letter telling him that he was an idiot and smudged with the tears Koala had spoken about. (Also with multiple doodles on his face, which he embarrassingly didn't notice until halfway through breakfast.)

Koala and Hack meanwhile took the chance to get to know Ace, and had taken to teasing Sabo about how his brother was a lot nicer than him. Honestly he was having trouble reconciling the unruly boy he remembered with the polite man his friends described, but there was no doubt in any of their minds that the person inhabiting Sabo's body during the switches was Ace.

His motorboat was named Striker, they told Sabo, and was powered using the Mera Mera no Mi. Sabo filed that useful piece of information away in case he needed a quick getaway during a switch. Ace was a member of the Whitebeard Pirates but was currently sailing alone in Paradise, in chase of a traitor who used to be in his crew. Blackbeard, none of them mentioned aloud, but knew all the same. That certainly narrowed down the time period considerably, and placed an uncomfortable mix of hope and trepidation in the pit of Sabo's stomach.

The first option that came to mind was to get Ace back into the Whitebeards' protection, but that action was quickly dashed. Without having any idea about Ace's current location, Sabo had no means of knowing whether following the direction of the log pose would bring him closer or further from the New World. Even if he did, it wasn't a journey that could be made in a single day, which was as long as the switches had lasted so far.

No, the intervention had to come in some other way.

His friends were wary of the potential repercussions of trying to change the past, and thus carefully steered clear of revealing to Ace anything about his fate, but Sabo knew that he would regret it for life if he didn't at least try. Because surely these switches were meant for something, right?

And Sabo would do everything in his power to make it work.

On the fourth switch, Sabo found himself in Impel Down, locked down by the strength-sapping bind of seastone shackles.

"Shit," he cursed very emphatically, mind already running at double speed to process the implications of this. And… (He couldn't stop the hope, not anymore.) And if this was finally his chance to do something.

"Ace-kun?"

Sabo blinked, only then realizing that he (Ace) was not alone in his cell.

Jinbe, Knight of the Sea, his mind quickly catalogued. Shichibukai, as of this time, though temporarily suspended and thrown into prison due to absolute refusal to fight against Whitebeard's crew. An ally.

"Jinbe-san… What I'm going to tell you now is going to be a little hard to believe, but I want you to hear me out."

This time when Sabo opened his eyes, it was different from the previous times. This time, he wasn't fully in control of Ace's body but instead watched from the background, as if through a haze. And he hated it, because this was the most important time of them all.

The battle raged all around them as Ace ran through the crumbling battlefield Marineford had become, fighting hand-in-hand with Luffy. Sabo could tell at a glance that losses on both sides were great even before they entered the final stage of the war. Whitebeard was making his last stand, holding the fort so that his children could get away, and Sabo felt awe at the sight of that proud back and at the lingering tremors beneath their feet.

Sabo had read Iva-san's report on the War of the Best in painstaking detail, going out of his way to talk to as many people who had been there as he could find, burning very moment into his mind. So much so that it sometimes almost felt like he had been there.

It was because of that that he exactly knew what came next, and almost like clockwork Akainu's voice crept up to them from behind, the words a clear insult. It didn't stop his heart from freezing as Ace stopped in his tracks like he already knew he would, turning back towards the Admiral.

"Ace…" he urged, but no sound passed those lips that were not his. "Please, Ace," he pleaded silently, not giving up even as terror gripped him, "Don't listen to him, take Luffy and leave this place. Get away from here, Ace!"

He watched helplessly as Ace's hand was burned by Akainu's magma, his fire unable to withstand it without the use of Haki. They were inching ever closer to the critical moment and just like watching a train-wreck Sabo saw Akainu loom over their little brother's unprotected form.

"LUFFY!" he yelled, desperation catching his voice, and perhaps it was that or perhaps it was because their emotions had become so in sync, but this time it finally reached.

The brunette startled, and Sabo felt himself settle into Ace's body with easy familiarity as they threw themselves forward. Armament Haki came to the surface instead of flames, it was that critical difference that stopped the magma in its tracks. Even so, Sabo knew that at his current level he would only be able to hold Akainu at bay for a few moments, but he was determined that those few moments would be enough.

He saw from the corner of his eyes as Jinbe bodily picked Luffy up to take him further from the fight. As expected though, the younger boy struggled, reaching out to his brother.

"ACE!"

"I'll follow in a sec, Luffy!" Sabo yelled back in assurance. With some effort he disengaged from his standstill with Akainu to dance away, settling quickly into a defensive stance as he watched the Admiral warily. Opposite him, Akainu's brow was furrowed deeply as he returned the stare in a new considering light. Sabo knew however that he was more disadvantaged here than he would have been in his own body, Ace's build and center of gravity different from his own. He wouldn't last in a proper fight against the Red Admiral.

Before either side could make a move though, blue flames erupted into their vision. Whitebeards' First Division Commander Marco the Phoenix entered the fray, unflinchingly countering Akainu hit for hit.

"Go!" he yelled back at them, and Sabo didn't need to hear it twice, running to catch up to Jinbe and Luffy.

Their younger brother was clearly relieved to see him and Sabo cracked back a smile at Luffy's wide grin of delight, so different from the hopeless catatonia from another lifetime.

They ended up on one of Whitebeards allied ships, where Sabo collapsed on the deck, chest heaving from exertion. Behind them, the jolly roger of the Red Hair Pirates flapped out strongly in the sharp breeze as Red-haired Shanks called for a stop to the war. Luffy had been hustled into the medical bay after fainting away the moment they left the battlefield, but the nurses had assured him that it was most likely primarily exhaustion. Sabo had waved away their attempts to give him a check-up as well and they eventually accepted his need for privacy, showing him to a room in the living quarters as they sailed away from Marineford.

Marineford. They were leaving Marineford.

Slightly hysterical chuckles bubbled up the moment he was fully alone, leaving his lips in garbled panting breaths that mingled into tears.

He'd done it. He'd actually done it. He saved Ace. Ace was alive.

And suddenly he wasn't lying down anymore, but sitting up a few feet from where he had been. He blinked at the shift, looking down at his body to find that he was himself again. Though not quite; he could already tell that rather than having a corporeal form, he was half-transparent like a spirit might be.

A sharp intake of breath next to him made his gaze snap over to meet dark eyes blown wide with surprise. The freckled man was staring at him. The… No, Ace. It was Ace, his brother.

Sabo was forgetting. Was this a side effect, a consequence of changing the past? Sabo had only regained his memories after the shock of finding out that Ace was dead. If Ace hadn't died, if Sabo hadn't seen that article…

But that was fine. It was fine if Sabo forgot, because Ace… Ace was alive. He was alive, and that was what mattered.

And Sabo… He…

What had happened?

He stared at his hand, the limb strangely translucent. Even as he watched, the colour faded further, yet oddly he felt no real worry at the sight.

"Sabo?" a voice whispered, the sound quavering a little. His eyes snapped up, honed in on the source.

Ace.

Again, Sabo felt a tug at his consciousness, the pull getting stronger with every second as his spirit or whatever form he was currently holding attempted to return to his body. And he knew without looking that he was fading away further, never having met to be there in this place and time.

"A…Ace." His words came out in a rush now, determined to be told before it became too late. Before he forgot them too. "I didn't go find you because I couldn't remember, and I only remembered because you died and I'm forgetting now again – Ace, I… It's stupid because you're alive and I should be happy but I'm forgetting and I…" His voice caught, breath stuttering as he voiced out the true worry that wracked his heart. "I – I don't want to lose you again."

A hand reached out to grab his, and Sabo briefly felt that flash of warmth as they made contact for the first time in more than a decade. But just like before Ace's fingers slipped straight through his incorporeal form, falling futilely past to grip only air.

Ace's eyes turned briefly stricken, before lighting up again with that familiar fiery determination.

"I'll go find you!" the brunette yelled. "Even if you're oceans away, even if you don't remember, even if I don't remember, I'll still find you! You know I will!" His hand reached out to him again, an uncompromising promise.

"SABO!"

"Hey~ Sabo-kun! What are you spacing out for?"

Sabo jumped at Koala's voice by his ear, turning quickly to see his friend standing next to him with her eyebrows raised. Seeing that she had gotten his attention back, Koala waved a clear file containing a stack of printed documents in front of his face. "Dragon-san has a new mission for us."

Shaking his head a little to clear it, he took the file from her, flipping through the documents quickly to get the gist. The detailed briefing would come later, as was the norm. "Right. We better get ready, then."

"What were you thinking about before, anyway?" Koala questioned as they walked quickly through HQ's familiar halls towards the living quarters to pack their things. "You looked really out of it for a bit there."

Sabo frowned, forehead wrinkling. It was a straightforward enough query, but somehow his mind was drawing blanks. What had he been doing before that?

"I… I'm not sure, was I asleep? I think I had… a dream?" That sounded right, but wrong as well.

Koala's eyes widened, her steps quickening so that she could turn to look up at his face. "Was it something from your past?" she asked. "Did you remember something?"

Was that it? A memory from the ten-year gap he had at the beginning of his life, those long-lost days before Dragon had saved him?

Sabo's brow creased as he tried to recall anything, absolutely anything, from the dream. Yet somehow…

"I… can't remember."

Two years earlier and a sea away, Ace opened his eyes to a vision filled with tears. His fingers touched his cheeks, coming away wet with moisture.

"Sabo?" he whispered, the name dispersing soundlessly into the silence. Had he dreamt about Sabo? He… It was strange, he couldn't really remember.

"Ace…" a voice mumbled, making Ace startle and look over in its direction. His gaze softened immediately when he found his younger brother lying in the bed next to him. Luffy was almost swathed from head to toe in bandages, a painful sight that sent a pang to Ace's heart, but the steady rise and fall of the boy's chest indicated that he was genuinely resting rather than in a coma. Luffy mumbled in his sleep again, Ace's name slipping past his lips.

Ace rubbed away the tears determinedly, reaching over to gently brush his younger brother's sweat-damp hair away from his face.

He had come so close to losing Luffy. He had lost so much that day, crewmates and friends and Oyaji… But he was selfish enough to thank the heavens or whatever guardian angels that watched over their fate that he hadn't lost Luffy as well. Maybe it was Sabo who was watching over them, who had protected them through that bloody battle.

His lips turned up slightly in a weak but genuine smile at the thought, the first since the war. Yeah, that sounded like something Sabo would do.

But even as Ace gently ran his hand through Luffy's hair, lulling the boy back to sleep, his heart continued to tell him that there was something, something important, that he had forgotten.

It was no more than a flash of dark blue, which ought to have been invisible in the bustling crowd in the town marketplace. But Ace's gaze honed in on it nevertheless, drinking in the sight that met his eyes. He knew that figure. Never mind that it had been twelve years, that they'd both grown almost beyond recognition from their childish days. Something in his memory instantly knew, there and then, that there was no doubt.

He pushed forward, almost stumbling through the crowd in his haste. Closer, closer, until Ace stood just a few feet away from that familiar yet unfamiliar back, almost close enough to touch.

"Sabo," he breathed.

The figure turned and their eyes met, and the responding name, spoken just as shakily and filled with emotion, made everything perfect again. "Ace."

Finally, after so long, it finally felt right.

"I remember."

*insert Kimi no Na wa ending song for maximum feels*

I really do recommend watching the original movie if you haven't, it's awesome.

I love how the themes of soulmates, time travel and diverging timelines fit in so well with OP-canonverse AceSabo, everything just seemed to fall perfectly in place and made this story a joy to write. (And I'd happily take any excuse to write alive!Ace, so that's always a bonus.)

Please review and let me know if you liked it as well!