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Run and Repeat
The moment Barry recognised the voice that had just spoken, his first thought was the terror of how exactly this man could be here. The notion that the Reverse Flash was capable of time travel was terrifying enough on its own, but considering how rarely he'd encountered the man so far he'd held out hope that his enemy's ability to actually use it was limited for some reason.
The fact that his enemy knew enough to find him here, when he hadn't done anything to make his presence in this time public, raised more than a few terrifying questions, but right now all Barry could focus on was keeping up with his enemy. Oliver might have managed to defeat him when he'd been provoked by Bivolo's powers, but back then Oliver had already trained with him a couple of times and had probably spent a few months working on incorporating anti-metahuman techniques into his training just in case. The Oliver of right now hadn't faced anything more serious than the Dark Archer (or whatever Malcolm Merlyn actually called himself), and if he couldn't beat that guy yet he'd at least have serious trouble with the one enemy Barry hadn't managed to defeat yet himself.
With those thoughts having raced across his mind in less time than it would take to read, Barry had already moved to attack the man in yellow before Oliver could react to the voice himself. Whether it was just a lucky shot or he had genuinely taken the other man by surprise, Barry forced his opponent out of the garage and into the road outside the Merlyn Mansion, but soon found himself chasing his foe into Starling City before he had time to come up with a more refined plan of attack.
His experience racing through the city when dealing with Digger Harkness's bombs at least gave him a basic idea of Starling City's layout, but he surprised himself when he found himself running through an area that he didn't immediately recognise. He soon realised that this must be the portion of the Glades that would be destroyed by the Markov Device in a few months, but the moment he spent slowing down to take that into account was enough for his opponent to catch up with him. As the Reverse-Flash launched a punch at his head, Barry surprised himself when he managed to parry and follow up with a blow of his own; the last couple of times he'd fought this man, Barry had always felt as though he was the one moving at a slower speed-
A kick to his chest forced him back and gave the man in yellow time to run down another street, leaving Barry to take a moment to get his breath back before he charged down the street after his enemy. He managed to put on an extra burst of speed when they passed an open area Barry recognised as Nelson Plaza, but couldn't entirely believe it when he managed to catch up with the man in yellow; either his enemy was baiting him for some reason, or the other speedster was genuinely slower now.
As the chase moved down another street, Barry saw a trio of men advancing on a young woman, their entire posture making it clear that they had malevolent intentions in mind, and diverted from his race after the man in yellow to knock the attackers down with a quick punch to the back of their heads before he picked up the race again. His still-unnamed foe was keeping up a good pace up ahead, but the longer this race went on the more certain he became that the Reverse Flash was just a bit slower than he had been when they'd fought around Christmas in the future. The more Barry pushed himself, the more he realised that he was gradually gaining on his opponent, just as the man in yellow seemed to grow ever-so-slightly slower with each passing step…
With each step forward, he found it harder to recall exactly where he was in Star City, but he never lost track of his final goal; he was going to catch up to the man in yellow, and he was going to get some answers about what his enemy was doing here, two years before his own debut as the Flash.
Actually, I should probably ask why he's so much slower now than he was when we fought at… was it Christmas?
Pushing those faltering thoughts aside, Barry redoubled his efforts to keep up with his enemy, until a desperate push gave him just enough of an edge to strike the yellow-clad speedster in the back and force his enemy into a tall building that Barry quickly realised from the dank smell and lack of personal items had been abandoned some time ago. The other man regained his balance in time to see Barry standing in front of the door and race up a flight of stairs, likely intending to find another way out, but Barry managed to keep up the pace and catch up with his foe just in time to knock his enemy off his feet before the other speedster could make for a window or start to head down again. Before the man in yellow could get back up, Barry stamped down hard on the man's ankle, coming to a halt when he heard his enemy let out a call of pain that made it clear he wouldn't be walking again any time soon.
"Got you," he said as he returned to more normal speed, panting from the exertion as he glared at his enemy.
"Impressive," the man in yellow said, his face and voice still vibrating as he looked up at Barry. "Especially considering your youth."
"…What?" Barry looked at the man, unable to hide his surprise that his age could have anything to do with what was going on right now. "What do you mean?"
"You didn't know my name, which means you aren't the Flash I thought you were…" the man in yellow said, the other speedster's arrogant grin still visible despite the vibration that hid his face from clear view. "When are you from?"
That simple statement threw Barry more than anything he'd expected to hear.
"When?" he repeated, looking at his foe with a new sense of cautious curiosity. "When am I from?"
"I thought you were the you that I was familiar with, but you're obviously a lot younger than him," the man in yellow explained, his tone surprisingly solemn as he got to his feet, the damage to his ankle clearly already healing. "You know enough about your powers that you clearly didn't just get them some way I don't know about, but…"
"Let me guess; older me has some tricks I haven't used against you yet?" Barry said with a bitter edge, grateful that he had already discussed the idea of his future self fighting this guy with Cisco and Joe so that the concept wasn't a total surprise to him. "That's why you attacked me when I was a kid and… and…"
"And what?" the Reverse-Flash asked, actually sounding curious as he looked at Barry with what he could have almost interpreted as genuine concern if it wasn't for the fact that this was the man who had killed his mother-
"Was… was I there?" Barry looked at the man in yellow with a new sense of uncertainty; it felt as though the thought was slipping from his mind the more he tried to hold on to it. "I mean, I know I was there in my past, but… was an older me there as well? Was I… he… trying to stop you?"
"You don't remember?" the Reverse-Flash sounded surprised at the question. "Even when you know enough to ask that question?"
"I… I think I knew… and now… it's like it vanished…" Barry said, not sure why he was being so open with his enemy even as he spoke. "I'm thinking of my past… and then it's missing…"
"Time travel," the Reverse-Flash observed, his tone becoming mocking once more. "You quantum-phased into yourself during an unplanned temporal jump, didn't you?"
"Quantum phased… is that why I basically possessed myself?" Barry had no idea why he was saying this much to someone he knew he hated, but at the same time the other speedster was the only one who might be able to understand the questions Barry still had about this screwed-up situation.
"Precisely," the man in yellow nodded with a sick sense of approval. "You jumped so precisely through time that you essentially phased into your past self's body when you entered this time period… and I can even explain your fading memory."
"Really?" Barry said, reminding himself not to completely trust anything this man had to say. "How does that work?"
"Your actions here are overwriting the future that you came from and everything you experienced in it," Barry's nemesis explained, a slightly mocking edge to his explanation. "The more you use your speed, the more you exhaust the energy reserve that you brought from your future into the present… along with the protection it grants your remaining memories."
"So… every time I use my powers back here, the faster I lose my speed and my memories?"
"Precisely," the man in yellow said.
"OK…" Barry said, hating to concede that he was relying on a known enemy for information even as everything he was hearing made sense. "And… what does this mean for my future?"
"That is where things become… interesting," the Reverse Flash said, an edge to his voice that reminded Barry of a man holding back the urge to laugh. "So long as you do nothing to affect the circumstances that gave you your speed, you can theoretically make other changes to history if you wish without it affecting your memories, but once you exhaust your speed reserves and your changes become permanent, essentially the source of your memories becomes a temporal remnant."
"A what?"
"Think of it as a 'clone' of yourself created through time travel, such as travelling back through time a few seconds so that the younger version of yourself can now do something different," the man in yellow explained, that same twisted sense of amusement in his voice. "It's an interesting temporal paradox, but so long as the paradox-created version of yourself dies, it will be a… minimal problem for the timeline to overcome."
"So you're saying… I'm a clone of myself who'd have to die to stabilise reality?"
"More that you are possessed by a clone of yourself that will eventually cease, but that's one way to view it."
"Right…" Barry said, taking a moment to think back over what his enemy had told him earlier to make sure he understood it. "You mean… since I merged with myself and I'm forgetting everything… there's no need for me to die?"
"Once your memory is lost, your life will unfold as though you were living it for the first time," the man in yellow said, before he stood up and flexed his shoulders with no sign of discomfort in his stance. "Which means that I no longer need to be here."
"What-?" Barry began before the man in yellow charged towards him, hitting Barry with such force that he found himself on the other side of a broken window before he had time to properly realise what had just happened. Mind flashing back to the trick he'd used to stop Kyle Nimbus, Barry turned around mid-air and began to rapidly spin his arms as he fell towards the ground, generating two small tornados that slowed his fall. As soon as he was close enough to the ground, he cut off the tornados and hit the ground, moving briskly around to make sure he hadn't damaged anything around the street before he ran around the area as quickly as he could.
Unfortunately, it only took him a few moments to confirm that the man in the yellow suit had vanished while he was busy saving himself, and Barry came to an abrupt halt when he realised that he couldn't remember the name of Joe's partner and Iris's new boyfriend in the future.
Great… he slammed his hand against the nearest wall in frustration. As if trying to stop the Undertaking wasn't enough pressure, now I've got to deal with an unknown time limit before I basically 'run out of juice'.
The idea of him being some kind of time-travel-created clone of himself was a disturbing one, but everything the man in yellow had told him basically lined up with what he'd been theorising about this situation so far. He already knew that the other man was a time traveller even if he didn't get how or why his enemy had come after him in the first place, and everything he'd been told made the kind of complicated sense that struck Barry as someone being honest even if it was confusing. He might work in the lab rather than in the field, but he was still sometimes called on to at least observe interrogations, and from what he'd seen, people lying under pressure tried to keep it simple; if the man in yellow was willing to give him that much detail, Barry was inclined to believe that he was being told the truth.
His mind made up in that regard, Barry took a moment to think over his immediate situation, but it didn't take long to decide what he was going to do next. If he was some kind of 'time-travel clone', everything he remembered of his actual life would eventually play out the way it should so long as he didn't do anything drastic like try to stop the particle accelerator explosion, and that wasn't exactly a practical concern when he couldn't exactly give anyone any evidence of what he'd be trying to tell them about.
If he only had a little time to help Oliver and Diggle before he would lose his memories and powers, he was going to make full use of that time by offering some aid to the people he could help…
"Well," Thawne mused as he returned his suit to its storage cupboard in his secret room in STAR Labs, "that was… productive enough."
He appreciated that he didn't know exactly what the Flash was doing in this time period, but he had enough discreet security systems set up that he should be alerted if Barry's presence here did anything that might attract a time wraith or similar temporal anomaly. So far anything Barry had done in the past could have only made a gradual impression on the timeline, but he didn't want to risk looking into it in depth with his speed in such a fragile state.
On the bright side, at least that talk had explained why the dregs of Speed Force energy that he had absorbed from Barry's apartment were so fragmentary. Considering that Barry Allen was basically a temporal remnant who'd merged with himself and was making an active effort to undo his exact timeline of origin, the time-traveller was already basically running on fumes, so any excess energy Thawne could get from him would have come from a limited source anyway.
All I have to do is stay away and let him run down the dregs on his own. He's stupidly heroic, but he's not stupid, he knows that he can't do anything to stop himself getting his powers, and if he's with Green Arrow, at least Queen won't let him come to any serious harm.
Thawne would concede that he didn't entirely like the idea of leaving Barry to make his own mistakes in this situation, but he couldn't risk exposing his true agenda when the particle accelerator was still a year away from completion. He had faith that Barry had enough of an understanding of temporal mechanics that he wouldn't do anything that would stop him becoming the Flash in case he got caught in a temporal loop paradox, and he clearly didn't know who was under the yellow mask from whatever point in the current timeline he had come from.
In other words, all Thawne had to do was have faith that Barry's allies wouldn't let him get killed and that Barry wouldn't try to stop the planned particle accelerator explosion, and he could focus on tracking the future via Gideon to make sure nothing went wrong until Barry came back to Central City.
Maybe it was a risk, but Thawne had to admit that he was intrigued to see how things were going to play out, considering what the news reports stated was destined to take place in Starling City in a few months…
