AN: Past this point, shit gets really weird...
The sun was now dipping down into the ocean, and the vibrant hues of twilight were now spreading across the heavens. From his spot in the sand, he could also see a full moon rising over the retaining wall. Izuku impatiently stared at his carbon copy.
"You still haven't answered my question. Who are you?"
"You." His copy answered, entirely confident in its truthfulness, "Just… a little further down the line."
Hmm… Time travel? Did he seriously expect Izuku to believe he was from the future?...
"I don't believe you," Izuku stated flatly.
As a quirk and hero otaku, he knew of many abilities that stretched the laws of physics to their very limit, but never in the history of humankind was there one that just outright ignored it and broke causality.
"Of course you don't. I knew that already." His other self shrugged. Oh boy, here we go with the word games… "Our favorite color is not actually green, it's blue, specifically the kind of blue that All Might's suit is – we never told anyone since we didn't want to out ourselves as chuuni otakus on top of being weaklings."
"That's peanuts. Kacchan knows that. Try again."
"Alright." His other self tsked, "When we were little, before we got our quirk, we used to make our mother put on that All Might video a hundred times before we went to bed. You know, the train rescue one? It probably got on mom's nerves hearing that–"
"Still not convinced," Izuku rolled his eyes, "You could've figured it out by looking at my Mom's old social media posts in one of the
dozens of internet archives from before she deleted her accounts."
"Really trying to play hardball, aren't you, me." His other self shook his head, "Alright, you made me do this. Hidden behind last year's algebra book, where mom can't find it, there is a hard drive where we keep a bunch of digitized doujins of Mirko taking it up–"
"Okay! Okay! You win! You're me!" Izuku screeched, red as a tomato.
As a growing teenage boy, his… er…
preferences were one of those things that no amount of torture would force him to divulge. If he could help it – he would take that secret to the grave and arrange in his will for that damn hard drive to be cremated with him.
"See, I knew you'd come around! Now, we can get to the actual lesson here." Future Izuku smiled, a piece of gum showing under the canines. Izuku only just now realized that his mirror image was chewing gum the entire time, "Please bear with me if I start rambling – I'm just passing this along straight from memory."
Izuku made a silent gesture, asking himself to get on with it.
"To put it simply, the big gimmick that our quirk slots into is
symmetry. I'm sure that you noticed that when you try using your quirk, the flickering copy you made looked flipped over? That's because you're actually mirroring it, not copying it; you are
reflecting that object across an invisible plane drawn between your hands." Future Izuku explained, "But, here's the kicker! You're not just reflecting it across space –
no, that would have been too easy, too
sane – you're reflecting it across space
and time."
"Hold up,
What!?" Izuku exclaimed.
"I'm not kidding. Remember the letter? How it acted all weird and did the opposite of what you expected it to do? That's because its arrow of time has been flipped sometime in the future, and well… I have a sneaking suspicion on who wrote it."
"Us?" Izuku hesitantly guessed. His brain was melting trying to process this new information.
"Yeah, but I don't know quite when yet – It's still in my future, relatively speaking." Future Izuku half talked to himself, and half talked to…
himself.
Izuku pinched the bridge of his note, "Okay, you're giving me one hell of a headache right now…"
"
Tell me about it…" His future self muttered bitterly, "Alright, let's try a different approach."
Future Izuku then proceeded to crouch down on the sand and draw a large L shape with arrows at each end… Wait, no, he had seen this in algebra class before – it was a coordinate plane of some kind.
"I tried to dumb this down as much as possible. But, I'm not God, and I can't understand it for you. This little graph I've drawn here is a simplified model of our universe: one dimension for space," He drew an 'S' right next to the vertical axis, "and one dimension for time" and a 'T' at the end of the horizontal.
"Now, let's place an object in this universe – could be anything, a pencil, a bookbag, hell, even a pack of gum," He put a finger in the sand and started drawing a squiggly line at a steady rate, "Whatever it is, our object here is doing normal object things, traveling through its one axis of freedom as time passes by. This path that this object traces through spacetime is what we would call a 'world line'" He stopped drawing when he reached near the end of the graph.
"I see…" Izuku scratched his hairless chin.
"Let's introduce our quirk into the equation." Future Izuku then drew a vertical at the world line's end and from that line, another line emerged, this one squiggling in the opposite direction in the time axis.
"It's going backwards?"
"Yes," His future self finished drawing once more, "In essence, what our quirk is is a mirror; not one that reflects light, but one that reflects world lines. You get the gist yet?"
"I… think so?" Izuku said without much confidence.
"Good enough…" His future self looked toward the sun, which had now fully dipped below the horizon, "Oh, looks like it's about time for a practical demonstration. Observe." He put both his hands in front, palms up.
In the blink of an eye, two packs of gum, the same kind that was in Izuku's left pocket right now, appeared in his future self's hands. One of them was reflected, having mirrored writing printed all over it, matching its normal counterpart.
"How did you do that?" Izuku asked, leaning in to get a better look.
"In theory, it's pretty simple." Future Izuku waved around the inverted pack, "One of us flipped this pack of gum's world line sometime in the future. All I did when I used my quirk was flip it back forward." He pointed back toward the normal pack of gum.
"Okay, one of us… But who?"
"Sorry, but that would be spoiling the lesson," His future self winked, "Now, lay your hands out like I did and try using your quirk. You should get a slight tingling when it's the right time…"
Izuku followed his future self's instructions and presented forth his hands. Impatiently, he tried to use his quirk, but nothing happened…
"It has to have already happened… or is going to happen… or will have happened–" His future self facepalmed, "God, human languages are not equipped for this bullshit quirk. Just… Try again in five seconds or so."
Okay then…
Izuku counted down in his head. Five… Four… Three… Two…
Once he reached two, he started feeling a slight sensation on his palms, a static feeling not unlike touching a doorknob after rubbing one's socks on the floor. It made his hands twitch, and almost uncontrollably, he used his quirk; two packs of gum appeared out of thin air, just like they did for his future self.
"Whoa…" Izuku set them down on top of the sand.
Wait, didn't his future self say that these weird reversed objects were actually going backwards in time?... Didn't that mean their physics were applied in reverse as well? Izuku pondered.
To test his hypothesis, he pulled out his phone and opened up the camera, pressing record. Then, he hovered his hand over the reflected pack of gum, making a grabbing motion. Suddenly, halfway before his hand was fully closed, the pack of gum flew upwards toward his hand. He stopped recording.
He placed the pack of gum back down again as he looked over the footage. Afterwards, he played it again, but in reverse. It wasn't flying up toward his hand, it was
falling from it.
A lightbulb exploded over Izuku's cranium – the revelation causing enlightenment and confused headaches in equal measure.
And all the while, his future self was giving an insufferably smug smile, "Now you're getting it!"
Why couldn't he have gotten something like firebreathing instead? It would have been a lot less trouble.
Then, out of the corner of his eye, Izuku caught something. Behind one of the many piles of rubble and rubbish, another figure emerged, walking backwards. Green curly hair, same dirty shirt… Now where did this one fit into the timeline?
"I'm assuming that's you coming over here," Izuku asked.
"As far as the world lines are concerned, and in his local perspective, he is in between you and me." His future self answered blithely, "How else did you think I got here? I didn't just pop into existence from a time machine like straight out of a bad sci-fi movie."
"Well, you don't have to be so smug about it." Izuku rolled his eyes.
"Trust me, you'll enjoy it when the time comes." Future Izuku smirked.
The backwards-walking Izuku had stopped near where they were sitting.
"…won edih og attog I ekil skool ,hA"
He spoke in a strange, impossible-to-describe tongue, utterly incomprehensible to Izuku, and then took his seat nearby. His future self made a shooing motion towards him before turning back to Izuku.
"Now, as that one pre-quirk era hero manga I can't remember the name of says, 'With great power comes great responsibility.'" Future Izuku started to lecture, "With our quirk, that means our responsibility is to preserve the worldlines of everything we interact with and make sure that they don't cause any unintended consequences to those in the past or future. Remember, just because something happened or will happen is not an excuse not to act. So, here's my task to you: try to figure out and resolve the worldline of this pack of gum." He laid out his pack of gum and its inverted duplicate right in front of Izuku's own.
Izuku stared at the four objects, trying to figure out where to begin. But, as his future self blew a bubble, an idea came to him. He opened up the normal pack of gum which he inverted and took a piece from it; chewing on it, a strong mint taste flooded his mouth, providing something to distract his mouth from his typical muttering.
He opened up the inverted copies of the pack, and it was still full, but the other one, which was given to him, had that exact same piece of gum missing; and so did its forward-going duplicate as well. He knew right then and there which one to reflect, and so he did, picking up the second inverted pack and the first forward pack and using his quirk, both of them disappearing under his grasp, leaving behind a tingling sensation.
"I knew you could do it!" Future Izuku congratulated, "However, you're not done yet – there is still one more thing to do…" He gestured toward Izuku's inverted duplicate.
Izuku glanced down and noticed that his backwards-going copy's right pocket was empty, while Izuku's left wasn't… That was where he was keeping his pack of gum. His inverted self started to reach out, and Izuku undropped the remaining inverted pack of gum and placed it in the former's hand, who proceeded to unpull it from his pocket.
",uoy rof taht teg emmeL"
Then, Inverted Izuku suddenly jolted, as if remembering something.
"I know that look on your face, you damn quirk otaku." Izuku's eye twitched, "You still have a couple more questions to pry from me…"
Izuku stared at his other for a split second at the blatant hypocrisy, before his irritation surrendered to curiosity, "But… What about cause and effect? Is that all broken because of my quirk?"
"Nah, the universe doesn't care which order cause and effect goes in, only that they both happen." His future self dismissed his concerns, "Think of it like a magnetic field: north cannot exist without south, effect cannot exist without cause. Do you think the earth gives a damn if the compass is flipped over?"
"…lleh sa ykaerf si sihT …nmaD"
Inverted Izuku started moving around, ending up in a position that eerily matched Izuku's own but mirrored; he was playing around with the sand. A faint tingle started growing in Izuku's hands.
"Oh… looks like it's almost your time," Future Izuku commented, "I think we have time for one more question."
"How did you know all this information?" Izuku asked quickly as the tingle grew more intense. He realized there was a paradox if this inverted Izuku would eventually become his future self, "Where did it come from?"
A classic bootstrap paradox.
"Because we just had this conversation." His future self gave a serene smile, "No more, no less…"
"…aohW"
Again, his future self reached out, this time toward Izuku's left hand. Izuku took it; it was cold to the touch.
And when the tingling static grew too much, Izuku let loose and used his quirk once more.
Izuku let go of his own hand, still cold to the touch. He glanced around – everything on the beach was flipped over… The writing on the tin can was printed in reverse, the last dregs of twilight rising in the… West?
The waves of the water were pulling away from the beach, a couple of seagulls gliding tail-first in strange patterns, and the gentle pull on his skin from the salty sea breeze… It was a mesmerizing sight. He could not help but say…
"Whoa…"
"…ssel on ,erom oN"
One of his selves started speaking- Oh right, he just had that conversation,
".noitasrevnoc siht dah ew esuaceB"
"?morf emoc ti did–"
Izuku tuned out the nonsensical backwards speech.
He shifted around, moving to a more comfortable position. But as he did, he saw that the sand was acting funny, almost as if it were anticipating his movements. He cupped his hand in the air, watching as the sand spurted out to pile onto it – little grains were slipping up between his fingers.
"Damn… This is freaky as hell…"
As his other two selves babbled along, Izuku took in the beautiful strangeness of the world around him. He continued playing with the sand, which had a strange precognitive mind of its own, and he also looked back toward the rising twilight, as the hues grew warmer and warmer…
".ukato kriuq nmad uoy ,ecaf ruoy ni kool taht wonk I"
Oh, right! The pack of gum!
"Lemme get that for you," Izuku muttered as he hurriedly pulled it out of his pocket and handed it over to his past self.
Another few minutes passed as the lesson was repeated in reverse; Izuku sat patiently as he awaited his cue. That cue would come in the form of his other making a 'shoo' motion – but, in reverse, it looked more like a 'come here'.
"Ah, looks like I gotta go hide now…"
He pushed himself up to his feet and started wandering over to the nearest pile of rubble, choosing a quieter spot to seclude himself. He didn't bother checking his phone for the time; he knew it would probably be screwed up and temporarily unusable from being inverted with him.
Thus, he just played with whatever was in reach – mostly just undropping various bits and bobs and unpouring the rainwater from a plastic cup that was left there.
Before he knew it, he was already face to face with himself…
",haeY"
"Already?" He'd thought it'd take longer before he would be the one giving the lesson.
Eh, oh well… Hopefully, he'll remember what the hell his future self was talking about – he was gonna need it in a minute or so.
His future walked backwards into position over on Izuku's left – that tingling sensation returned, just as intense as before. Not fighting it, he used his quirk, and in an instant, the world was back to normal. He looked back at his inverted self.
"?ydaerlA"
"Yeah," He sighed.
Walking out of the rubble, he took a deep breath to calm his nerves. In the clearing, he saw himself talking in the ocean view.
Izuku slowly walked up behind and…
Tap. Tap.
