A/N: For some reason I've been obsessed with this crossover lately and have been eager to get my hands on anything related to it. (It helps that there's some really good stuff out there.) Naturally, that means that I got tempted to write it.

Honestly, I have no idea where this is going. It all started with "Killua looked accross the street, eyes sharp" and then I was kind of like okay let's actually write something and a picture came tumbling together. I don't really want to follow the MHA anime closely at all, so I'm just going to loosely write this without much MHA timeline research other than character investigation and power consistency stuff. We'll see how it goes.

Lmk if there's anything you're interested in seeing in this story because everything still kind of up for grabs and in the air.

(Shoutout: title is inspired by my new kitten whomst was adopted the previous day. He was sleeping as I was writing this.)


A Kitten In A World Of Heroes

(he has sharp claws and is very hungry)

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Chapter One: Arrival


Killua looked across the street, eyes sharp and cat-like. The streets were different, wider, more gray, he noted. There were no colorful bubbly street stalls; all the stores were packed behind tall layers of concrete and glass.

The sky matched the similarly dull gray tone – and it was what, midday? Barely anyone was walking around either. Boring, he thought. And all wrong.

Just where am I? he wondered, not for the first time.

"Yo, kid."

He looked back, an annoyed expression on his face. "What?"

It was Aizawa, the man who had caught him snagging a bento box from a small store marked "Seven Eleven" in strangely large red signs. Killua had the misfortune of having tried it in a store with someone with sharp eyes; though he could've sworn no one was paying attention to him, he had obviously overlooked the haggard homeless-looking man in the back.

For some reason, the guy had decided he needed to stop Killua, and had clasped his arm on the boy's shoulder, firmly told him to stop, then directed him to the counter and forced him to return the bento box and apologize. The shopkeeper had taken one look at the homeless-looking man – Aizawa he had called him – and deferred to him. Since Killua hadn't had any reason to cause any trouble, he let himself then be led outside, and so here he was, lingering on the street, hungry, the man still lurking behind him for some reason.

Killua didn't get what was going on. He had been minding his own business, trying to beat Gon at collecting money for the auction at Yorknew, when he had suddenly been attacked by an angry-faced lady. Something about being televised on the Heaven's Arena matches. She had called him a murderer. Then she had come at him with some big nen blast, and suddenly he was here, in this city that was all wrong and different.

It bugged him. It really, really bugged him that he didn't even know why.

"You realize I'm going to have to tell your parents about this, right?" the man said, expression flat. "We can't just have kids going around stealing things."

Killua shrugged, turned around to face the man fully, and smiled innocently. "I wasn't stealing."

The haggard man raised a wordless eyebrow.

"I was just hungry," he explained, maintaining the smile. "And took the bento box outside to eat it. I was going to pay it back when I got the money, I swear."

(He probably wouldn't have, but this man didn't need to know that.)

The man sighed, then slapped his face with a hand, dragging it down in a slow, exasperated motion. "Kid, that's still stealing." His expression turned flat. "Look, tell me where your parents are, and I'll work things out with them. Otherwise, I'll have to get the police involved."

Killua looked at him like he was stupid. "Huuh? The police? What are they going to do about it?"

The strangest expression flitted across Aizawa's face.

Killua's stomach growled though, so he didn't think about it for long. No, he sensed an opportunity here.

"Hey, Mister Aizawa," he said, "since you stopped me from getting food, mind buying something for me?" He put on his sweetest smile. "I'll make it up to you later!"

Aizawa stared at him for a long moment.

"You don't have parents, do you," he said.

Killua mocked taking great offense at that, eyebrows furrowing tearfully, pressing a hand against his chest dramatically. "What? I have parents. I just left them because they're controlling asshats."

The man's expression turned even more sombre. "Look, kid…"

Killua sighed.

"Look, old man," he said, "I don't really get what you are trying to do, but I'm a Hunter, alright? A Hunter." It wasn't quite strictly true, but if it came down to it, he could say he had pawned his license for money and get Gon to back him up. After all, the new phones Lerio had got them were supposed to be universally connected. "So you don't need to call the police. I told the clerk I was sorry, anyway. Are we done here?"

If anything, the man's expression had only grown irate as Killua spoke.

"You're one snarky kid," he said, voice lower, standing over him threateningly. Any sympathy on his face had vanished. "Being a 'hunter' or whatever does not excuse you from the law. Now, you have two choices, I can either – "

"You don't know what a Hunter is," Killua realized aloud, surprised, interrupting the man's ultimatum. He took a step back, frowning, looking around. "Where really am I?" he muttered.

Killua's reaction disconcerted the man for a second, but only a second. The man swiped for Killua's arm.

"Woah, woah!" Killua danced backwards, narrowly avoiding it. "What are you doing?" He narrowed his eyes at the man. "You trying to kidnap me?"

The man frowned, growled, then pulled out some weirdly stiff bandages he had wrapped around his neck. "I'm warning you, kid. I didn't want to get my status involved in this, but I'm a pro hero. Eraser Head. You can't fight this. You have to take responsibility for trying to steal something."

Killua shook his head in amusement, putting his hands in his pockets casually to show just how unimpressed by the titalage he was. "Pro hero? That sounds like something out of Milluki's comic books."

Then, getting an idea, he grinned at the man impishly, stuck out his tongue, and said, "See if you can catch me then, hero!"

Killua turned and ran.

Of course, Aizawa followed.

It was the most fun Killua'd had in a while – well, that wasn't true, not with him and Gon messing around together in Heaven's Arena – but still. This Aizawa-guy was surprisingly good; he kept up even as Killua ducked and dodged through alleyways. What was more impressive was that this guy wasn't using nen at all; he had checked his aura with Gyo and even though it was fluctuating weirdly a bit, there was no clear control over it at all. This guy wasn't a nen user.

Grinning, Killua decided to push it a little more. He channeled some aura to his feet, just a bit, making his bounds longer and more effective. He glanced up a nearby fire escape. Maybe he'd try to –

Abruptly, his nen flow was cut, slammed into zetsu.

Killua's eyes widened, and embarrassingly, taken by surprise, he stumbled. At the speed he was going at, it sent him spinning and tumbling into the nearest boundary, which happened to be a dumpster. It cushioned his impact, barely, resounding back and forth like a drum as he bounced off it and onto the asphalt floor.

"What the heck…" he mumbled, getting to his feet. He winced; it hurt. He turned to stare at the man standing at the opening of the alleyway, blocking the dim light. Aizawa was staring straight at him. "You did that!?"

"Usage of your quirk is forbidden in public without a license," the man said sternly. "Especially for escaping responsibility for your crimes."

Killua felt vulnerable, forced into zetsu like this. Any hit he'd take he'd feel ten times worse, and he already felt that hit into the wall much worse than he normally would have. His body's natural protection had been utterly shut off. He was lucky he hadn't broken bones.

What a crazy nen power. He hadn't even known something like that was possible.

"Okay, I'm taking you seriously," Killua said after a moment, eyeing the man warily. "Who are you? What do you want?"

"I'm not trying to hurt you, kid," the man said. He spoke slowly, but his expression was entirely alert now, invested. It was a shock compared to the haggard, tired man he was speaking to earlier. "Come with me, and I can help you sort out your family situation. Heroes like me are here to help you."

Killua snorted, glaring at him. "If you're here to help, stop doing whatever you're doing."

The man stared at him for a moment, then suddenly, his nen sprung back to life. Killua stood straighter, flexed his aura, and sighed in relief.

Even before Wing had activated his nen, his body had always had a natural invisible layer of protection. It just felt wrong to have it forcibly suppressed. Worse, Killua could be in real trouble if that wasn't all this man had up his sleeve. If the man had deliberately disguised his nen ability earlier… who knew what else he was hiding?

"Thanks," Killua finally said, grudgingly, keeping his eyes targeted on the man, watchful for any sign of threats. "I guess I'll hear you out. But first, really - what are you talking about? Heroes? Helping? Where am I?"

"Musutafu," the man said shortly, though a hint of confusion showed in his voice. "Pro heroes like me are meant to keep the peace and fight against villains." A pause, in which he looked at Killua's blank expression. "You… really don't know, kid?"

Killua shook his head, frustrated. "What is Musutafu? It sounds like a soup."

Again, that strange expression flitted across the man's face. Killua could see it from here, all across the alleyway.

"Near Tokyo," Aizawa clarified finally.

Killua rolled his eyes. That hadn't been very helpful. "Right, and that sounds like a bad name for a hipster clock company."

"Kid… you're not seriously pulling a prank on me, are you?"

Killua stared at him. "Just tell me what country I'm in."

"... Japan."

Killua swore. "Fuck."

That was so far from Yorknew city! How was he going to get back in time for the auction?

"Listen, old man," Killua said impatiently. "Where can I find the nearest blimp? I need to get back to Yorknew city. There's an auction, and I need to get back to my friend…"

He trailed off, getting a bad feeling when he saw the man's expression grow concerned in a way that had nothing to do with telling him where the nearest blimp was.

"You mean… New York?" the man said, sounding perplexed. "Look, kid, I don't know what you're…"

Killua stopped paying attention.

New - York?

Suddenly, it clicked.

The different money system, the way the clerk at the first store had looked at his Jenny so strangely and called it "foreign currency" even though Jenny was supposed to be accepted everywhere civilized. The different cars, the different streets, the weird signage. Aizawa's lack of recognition at the word "Hunter", the utter sense of miscommunication they were having. The strange mention of "pro heroes", the implied assumption of obviousness. Even the mysterious Japan Killua had heard of wasn't supposed to be this different from the rest of the world. Even they were supposed to know about the Hunters – Hanzo had, after all.

Combined together, these facts led Killua to a very bizarre, very unbelievable conclusion.

No, it can't be.

"Old man," he said abruptly, interrupting whatever he was saying. His thoughts were wild. "You know what the Hunter's Association is, right? Or… Zaban City? Kukan'yu kingdom? It should be close to here." His voice grew more desperate as he watched the stranger's face fail to light up in recognition.

No, he thought. This really can't be happening.

"Kid, I really have no idea what you're talking about."

Killua pulled his phone, the turtle shell Leorio had got him. Ignoring the man's sharp reaction, he hurriedly dialed Gon's number, eyes wide.

It didn't even ring once. Just, nothing. "Service error", it said.

He tried Leorio's. Same thing.

Calm down, he told himself. Maybe it isn't universal after all.

Just where had that woman sent him?

He looked up, saw that the man had approached. Panic was making him sloppy. He leaped backwards. Later. He'd worry about it later. For now, he needed to get out of here, reequilibriate, figure out what to do.

"I really need to get back," he said. "I can't just have, have disappeared."

He wasn't sure if he was talking to himself or to the man.

"Let me help you," the man said, walking and talking slowly, like he was approaching a wild animal.

"No," Killua said sharply. He turned on his Gyo, sending aura to his eyes. He had been right before – no trace of nen control. The man would have no reason to hide it now.

He swallowed. Another world, unfamiliar surroundings – if his picture of the situation was right – then that meant that whatever that was, that shut him into zetsu, was probably something else. A complete unknown.

"I'll figure out my own way," he said, backing away, trying to sound casual. He looked up; above the dumpster was a fire escape. Ten stories high to the roof.

It'd be tricky with his aura suppressed, but he'd have to risk it. Though he seemed willing to talk, this man was too dangerous and too obviously wanted to control him for Killua to risk staying around him. If Killua was right – and he was almost sure he was right at this point – he didn't want to find himself stuck with the one person he'd have trouble escaping from, when he was in a world of unknowns.

He took another step back, pressing his back into the dumpster.

Aizawa took a step forward.

Killua stilled.

He took a breath, and –

Launched into motion.

He kicked back against the dumpster, flipping midair to land on top of the dumpster. He leapt into the air, grabbing the lowest rung of the fire escape, then launched himself up five rungs at a time. No zetsu yet, good; the nen-shutting man must have not yet processed the move.

By the time he had reached the top of the last ladder, only seconds later, however, zetsu had been slammed upon him again. Chancing a glance down, he saw that Aizawa was just barely reacting, only beginning to throw his weirdly solid bandages at him.

Killua grimaced. He leapt upwards again, using less than what should have been his natural strength, and gripped the rooftop tiles. It took far too much effort, and too many precious instants, to haul himself up. Was this was zetsu was like, when it wasn't just being used for stealth? The man's banadage-things just barely missed snatching at his foot, and he hadn't been looking forward to figuring out what they'd do to him.

Once he was on the roof, he dashed forward, leaping ahead as fast as he could to put some distance between him and the man. Gloriously, he felt himself reemerge out of zetsu, and used it to power his movements beyond what he had done earlier, breaking roof tiles so that he could leap thousands of feet at a time.

After a minute of this he decided it was high time to get out of sight by rooftop, and hastily jumped down to the nearest fire escape, and then down to another small alleyway.

He then hid himself, getting behind a box of crates that had been left out, purposefully going into zetsu. And waited. And waited, still in the way only a trained assassin could be.

A half hour later, with no signs of pursuit, he was certain that he was home free. He had escaped the nen-shutting man.

Killua breathed a sigh of relief, and got to his feet.

Who was he? he wondered, rubbing his arm. If I am really in another world… how many other people can do that? Was it just freak back luck to run into him, or…

He swallowed, a tight grin on his face.

Or did I just end up with really bad luck and end up in a world full of these guys?

Heart pounding in a way it hadn't in years, he slipped back from the alleyway into the main street.

What he saw there, however, made him immediately freeze.

It was daylight now, and the street was packed.

With monsters.

Blue-skinned, green-skinned, animal-shaped, eye-ball popping humans, whatever the imagination could conjure - they were all there.

And the ordinary-looking people amongst them weren't even giving the aberrations a second glance.

What was it that that nen-shutting guy, Aizawa had said? That word he couldn't identify? Quirk? "Usage of your quirk in public is not allowed…"

Either way, he decided, looking side to side, it didn't look like anybody was threatening him or anything, so it was probably fine for now. He'd figure out things as he went and figure out what was going on here. Wasn't the weirdest thing he'd seen, anyway.

His stomach growled again, complaining.

Damn it, he was too hungry for this. Too hungry to be dealing with the reality that he was in an alternate universe, an alternate dimension, and alternate whatever.

He strolled inside another "Seven Eleven" (they were common here, weren't they?) and used a walking assassination technique to disguise his presence. This time, he double checked to make sure there weren't any mysterious homeless men hanging around or any otherwise sharp eyes. When he was sure of it, he grabbed a bento box and strolled out, ready to finally eat his dinner.

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Added A/N: Heyo. This is the only time I'll have an A/N at the end of a chapter, because I've gotten many comments on Killua's versus Aizawa's power levels. [Minor spoilers ahead.] There are slight AU elements that will be explored as the story goes on. So if you're curious about why Aizawa's quirk affected Killua's nen, you should be able to get some answers – or more questions – as the story goes on. Strength-wise/speed-wise, I recently fixed some details that made it clearer as to what's going on with the fire escape episode (previously Killua's perceptions and frustrations gave off the impression that he was weaker than he was), but it's really that Aizawa is probably much stronger than you expect than Killua is weaker. Ofc some numbers have to be handwaved and fudged, but, well... I used my best judgement.

If this really does overly concern you, that the HxH world is not overly OP over the MHA world, then this story is not probably not for you, sorry. Strength-wise, between the two worlds, I have considered biology, canon speedfeats, etc. – but the truth is, no one agrees on this stuff anyway because stories are all about /impression/ and /perception/ rather than strict fact – especially in a genre like fantasy. There's no point in going further into it here, as even if I explained my reasoning and rationale to every single one of you, those who disagree will likely still disagree for their own reasons. Ultimately, I will try to be self-consistent and that is all I will promise you.

Final request: While I'd usually ask for comments on everything and anything, no matter how blunt, I'm actually going to ask for less comments on the ch1 power scale, just because I've heard it so much and it's no longer productive at this point. Feel free to make any comments about anything, including power scales, after ch1.

-ShadowPillow

Edit 6/11/2021: Alright, one last thing. I am doing a heavy REVISION of the story, introducing new scenes, deleting more redundant scenes, and generally improving the story. If you want to wait for it, this will be posted in a separate document in a few months. I believe the next time I post an update on this story, the revision for part one of the story will be complete. (Note that there are three total parts to the story. Part 2 is currently in progress.)

It's not a rewrite – just a heavy revision – but it does focus a lot more on Killua's adventures earlier on in the story with a bit more detail. That's all I can say here, if you want to read on now or wait until later, it's up to you. The revision should be sufficiently different to be interesting even if you read the entire story now, and any comments you make on this rawer version of the story will likely factor into the revision in some way or another.