Haha gosh this story is written in a style I'm really not used to, so there we are. It's also really choppy and written in a rush of "God I don't want to do finals hey let's write a story instead!" I just really wanted a "Tsuna learns to get along with the sibling he never had" kind of thing, and it's always fun to throw original canon Tsuna into fish out of water scenarios.

The Ten-Year Paradox

First Step: Destroy the Future

Between the slowly dissipating smoke and alarmed shouting of voices, Tsuna sighs, mentally strikes out "grape candy" from the grocery list, and makes a resolution to cut Lambo's allowance. For whatever good that will do.

But when he comes face to barrel of a handgun, Tsuna squeaks in a particularly un-mafioso like manner and dodges just in time as the bullet streaks past his cheek. It stings, but Tsuna is hardly paying attention to that, hyper mode sliding into place. He equips his Vongola gear and shoots upwards into the air to assess his situation.

He's outside, Tsuna notes. There are around fifteen men in black suits with guns.

It's broad daylight; what do these men think they're doing, attacking his twenty-seven year old self so openly?

The intersection they're on looks startlingly familiar – it's the one he rounds when visiting his mom. Except the trees look oddly short. Why is he being targeted in Namimori?

Tsuna's flames calm him, hyper-focusing him on his situation. Right. He can think about this later. Right now these men are in a civilian neighborhood with illegal weapons, attempting to kill him.

None of the Mafiosi – because what else could they be but? – think to look up.

(Another oddity; there were few in the mafia world who did not know the Vongola Decimo fought mostly airborne. Anyone with enough sense would have looked up first before anything else.)

Taking his chance, Tsuna throws himself between the men, aiming to knock-out, rather than damage. A few well placed hand chops to the back of the head later, Tsuna lands quietly on his toes behind the men.

They fall over, unconscious.

Hyper mode fizzles out on Tsuna's forehead. He takes a deep breath, stemming his oncoming panic attack as long as he can.

"Hieeeeeee!"

There were Mafiosi! In Namimori! How did they get past Hibari? How did they get past their Shouichi-Spanner-Giannini fortified security system? Moreover wasn't this the future? That was the Ten Year Bazooka's smoke wasn't it?

Tsuna's head swims with questions. And worries. Of the few trips to the future Tsuna has had in his lifetime, very few spoke of sunshine and rainbows. Or rather none did, but now that Byakuran was a kind-of-friend rather than enemy, Tsuna had hoped things like this wouldn't happen anymore.

There is blood on the ground where Tsuna first arrived on – there is no doubt as to whose blood that is.

Tsuna feels faint.

At the very least, his five minutes are almost over. Hopefully this won't be his future.

Going down to such attackers – what would Reborn say?

Right before Tsuna disappears in a puff of smoke, he thinks he hears a soft voice calling him.

"Tsu-kun?"

He's. He's vaguely horrified.

"That was Mom…!" Tsuna whispers, mortified, and hides his head in his hands. Out of all the ways for his mother to get involved in this awful business – !

But wow had his mom aged well. She looked ten years younger, never mind ten years older! She even had her hair long like she used to when Tsuna was... younger….

Tsuna pauses in his train of thought, suddenly realizing where he is. It's the same intersection he'd just been in. The trees are taller, the Mafiosi and the blood are gone, but it's definitely the same street Tsuna had been on.

He should have been returned to wherever his ten year later self had been, right?

Why is he in the same location as ten years before?

So the real paradox of the Ten Year Bazooka is that the future the user is transported to isn't their future at all.

It goes like this: every time the bazooka is used, the self from the direct future line ten years from that moment is sent back in time to the time the bazooka is used from. In the meantime, new decisions are made, infinitely more parallel verses are created, and when five minutes are over, the future self is sent to the direct future line before all these decisions have been made and the past self is returned from the last direct future line connected from the past.

Basically the direct future line isn't direct any more but a parallel universe that will never happen in this universe, and the past self returns to an entirely different current universe and timeline than once it left.

Or something. Gokudera said much more after that, but it was hard to follow as was.

In other words, despite all the years Lambo used the bazooka, never once did their Lambo ever get called back to the past.

It's an… odd idea. After all, if their direct past isn't the timeline to connect directly to their present, then what time does? There was some quantum mechanic principle that had to do with this, but as far as Tsuna is concerned, it just means that he doesn't have to worry about Lambo being left suddenly vulnerable because of something his younger self did in a fit of temper.

It does make him wonder what kind of Lambo would come out if they used some kind of Reverse Ten Year Bazooka though.

"The dangers of something stupid like that would change this present, you realize, right?" Reborn pins the edge of Tsuna's suit jacket with an expertly thrown fountain pen to the back of the plush leather chair, and Tsuna strangles out a startled squeak. "Don't think stupid things and do your work, Loser-Tsuna." Reborn admonishes, leaving his own stack of papers in a loud flop of manila folders.

Hyperventilating, Tsuna manages out, "Please tell me this pen isn't from the Pesca Boss' desk or something."

"It is."

Tsuna wheezes.

"It's okay – they'll be handing over half their possessions to us in a week as part of their debt payment anyways," Reborn reasons unreasonably.

"To the bank, you mean," Tsuna tries.

Reborn raises an eyebrow, "The bank Vongola ru – "

"Oh my god, Reborn, I'm trying to run a legitimate trade here please stop referring to businesses we support as ours." Tsuna nearly dies as Reborn aims and shoots unerringly at the head of the chair.

"The bank the Vongola run," Reborn says, very pointedly, "Don't think sugarcoating the way you reference things is going to make them any less illegal, No-Good-Tsuna. You've got a long way to go before you can claim anything like those bold statements of yours."

Tsuna makes a pathetic sound. "Yessir."

There's something definitely wrong.

It's something even Tsuna can figure out, hyperactive intuition or no. He plops himself onto the ground, vaguely aware he's in the middle of the street, but his existential crisis is currently more important than whatever hypothetical traffic he may block.

Thinking is not Tsuna's strongest point, so he tries to start from the beginning.

There was… smoke. From the Ten-Year-Bazooka. Yes. Probably.

His ten-year-later future involved (will involve?) him being cornered by Mafiosi and shot. Possibly. (There was blood on the ground, but Tsuna is. Not. Thinking about that. Not now.)

When the effects of the bazooka wore off, Tsuna was still in the same spot he'd just been in. Though in a possibly different time.

This should be his time now. The correct time. Date. Year.

Tsuna decides to stick to the optimistic view on his situation and makes for the office building Nono had bought out for them downtown as temporary Japanese Vongola base while Hibari (and Tsuna, but largely Hibari) muscled out the rights to build an underground base underneath Namimori.

(Tsuna, determined to stick to his Legal Vongola plan as long as he could, vehemently denied any offers from his father to ah. "Make" the landowners hand over rights. For free.)

The offices belong to a small realtor company and are you interested in finding an apartment nearby, sir?

Tsuna politely refuses their offers, his mind a thousand miles away.

M-maybe he got the wrong building? But no, the address is right, and Tsuna can see from the nearest window that the adjacent buildings aren't Vongola either.

This doesn't make sense.

"I-I'm sorry," Tsuna says, between the realtor encouraging him to come look at the layout for the new apartment building complex being built, "But ah, what is the date today?"

"It's the seventh of July, sir," the realtor recites faithfuly.

"And the year?" Tsuna adds, slightly apprehensive.

The relator looks at Tsuna funny, but answers his question anyways.

Tsuna feels his blood run cold, and his hyper intuition screams at him.

It is. The right date. The right time. After his mishap, the bazooka had taken Tsuna back to his right time, down to the hour.

Then why is Vongola not there?

Desperate to reassure himself that he hasn't gone nuts or forgotten something, Tsuna traces his steps through his neighborhood. The shopping district looks no different from before, the neighbor's Chihuahua is still there, terrifying as ever, and as Tsuna approaches the schools, he even sees Hibari! Who looks no different, thank god.

"Hibari-san?" Tsuna asks, relieved to find a familiar face, "Hibari-san do you know what happened to the base? Did something happen? How long was I gone?" Maybe. Maybe he heard the person wrong! The bazooka could have sent him into the wrong time or something. Something.

Hibari, tenses in the way that he does when a new face approaches him and growls, threatening, "What base? Who are you?"

Tsuna freezes, "D-don't make such bad jokes, Hibari-san – it's me! Sawada Tsunayoshi? You terrorized me all through middle school and high school!" He's his (unwitting) Guardian!

Hibari frowns at him, tonfas already out, "I don't remember such a herbivore attending these schools. Who are you?"

Tsuna barely dodges Hibari's first attack, still stricken at the information.

Hibari might not like him very much, but he would never feign to be strangers. There is. Something not right. Very not right.

Tsuna flees.

What was that?!

Tsuna stops running only when he stops feeling Hibari's killing intent. And then runs a whole five blocks more, just in case.

Tsuna leans against the nearest wall for a full minute before he realizes where he is. This is his home. He really is a whimp, running straight for his mother without even thinking about it. Really. The next time Lambo calls him loser, he'd deserve it – wait.

Tsuna turns towards the mailbox, breath hitching.

Another family's nameplate sits where "Sawada" is supposed to be.

Tsuna is definitely certain that this is his home. This isn't like the office that looks the same as any other office building downtown. This is his home, the one he's lived in for the past seventeen years of his life.

Tsuna takes a deep breath. This was it. He finally lost it. Reborn finally hit him hard enough to kill brain cells and induce artificial memory loss, dementia, something.

Or.

Tsuna tries really hard not to come to this conclusion, but there's something that has to be said about strange, illogical situations in his life.

The Ten-Year-Bazooka hadn't taken him to the future at all.

Maybe it'd taken Tsuna to the past.

Tsuna stares apprehensively as Gokudera's bombs emit sparkles at him.

"Tenth, I don't care if he helped us in the future," Gokudera says, anger thinly veiled, "I say we get rid of him right now before he can do us more damage."

Gokudera's hands twitch towards his belt buckle – towards his Vongola Gear – and Tsuna pulls out his best "please don't blow anything up" face.

"G-gokudera-kun! Don't be hasty. I'm sure Giannini didn't mean anything wrong by it – and he really does become an amazing inventor in the future! He's been working the hardest out of all of us to become the kind of person he'd been in that time," Tsuna soothes, wondering where Yamamoto is. He's much better at derailing Gokudera. Or incensing him. Nevermind. "We should give him a chance. Besides, this is also why we have Spanner and Shouichi-kun too. I thought I told Gianinni to lay off the weapons…."

A thought occurs to Tsuna.

"Er, he didn't happen to. Uh. 'Upgrade' anything else, did he…?"

"Hey guys! Look!" Yamamoto saunters in, holding a. Is that a sword? Why is it bending like that. "Gianinni said he made my sword more flexible, but this looks like it's too bendy, huh? Good thing I left Shigure Kintoki with my dad. Haha!"

To save himself more headache, Tsuna makes the executive decision to confiscate everyone's weapons for the time being.

He hadn't gotten to Lambo yet before the bazooka blew up in his face.

So.

So.

That time with the Mafiosi. That could have been the past.

Except Tsuna doesn't remember ever having encountered anything like that when he was younger, and he definitely doesn't remember ever being shot. Well. Before Reborn, that is.

So then, just where had the Ten-Year-Bazooka taken him to?

There was also something else. Something about the dangers of a backwards Ten-Year-Bazooka. Reborn had said something to Tsuna about changing the direct past line. Something about…

"The dangers of something stupid like that would change this present, you realize, right?"

Change this present. Tsuna would have made his present into a parallel world from the direct future line his time connected to with the Ten-Year-Bazooka.

So.

Maybe he was in a parallel world?

… Or this could be his world and he'd just completely, accidentally obliterated his future. Present.

… Think positive, Tsuna.

If it's parallel worlds, there's at least one person Tsuna knows he can talk to.

Hoping to god he has enough change to work a pay phone, and that Byakuran has the same cell number in this odd place, Tsuna fumbles out his wallet and walks toward the nearest phone booth.