Chapter 1: Katzuku

Quirks.

Ever since that first miraculous child was born nearly two-hundred years ago, people throughout the world have developed incredible powers and abilities once only seen in fairy tales and comic books. Such abilities, called Quirks, are developed around the age of four. Most are rather passive, but a lucky few are gifted with a Quirk of incredible power. From manipulating the elements, to overwhelming strength, to affecting the minds of those near; the possibilities are literally endless.

And when they appear, it can be quite a shock for an unexpecting child. Even more so as they first learn how to use it.

Izuku Midoriya is one such child.

It was a peaceful morning in the Midoriya household. Inko Midoriya was washing dishes in the kitchen of her modest apartment. It was small, but homey, the walls covered in pictures of her and her son Izuku.

Every few seconds, Inko would look over her shoulder, keeping an eye on Izuku as he played in the living room. He was in the middle of his Saturday morning cartoons, reenacting the colorful action on screen with his favorite toy, an action figure of the hero All Might. Inko smiled to herself as he laughed and played, hopping around in his footy pajamas styled to look like the number one hero, his green hair curling out of the hoody.

"Never fear, citizens! This villain shall threaten you no more! Why? Because I am here!"

Inko chuckled to herself as Izuku started chanting 'All Might! All Might' under his breath, a childish recreation of a cheering crowd.

Yes, a normal peaceful morning, unlike any other.

Then… it happened.

Inko saw a brief flash of green light out the corner of her eye. She turned her head in surprise, looking for the source, but all she saw was Izuku facing the TV, coming to a stop as something drew his attention. Thinking the flash had just been from the TV, Inko went back to scrubbing their breakfast plates-

"MOMMY!"

Inko's heart leapt into her throat as Izuku let out a panicked wail. She whirled around, only to find Izuku running towards her as he clutched at his right hand against his chest. She knelt down to him instantly, completely forgetting her sopping hands as she put them on his shoulders. "Izuku! Izuku, what's wrong, sweetie?"

Izuku stared up at her, his panicked green eyes brimming with tears. "My hand ate All Might!"

...

Inko blinked at him, taking a moment to register what he'd said. "W-What?" She asked haltingly, a slight laugh of bemusement escaping her.

Izuku just sniffed, then showed her his hand. "Look!"

Inko couldn't help but let out a sharp gasp as she saw her son's hand. His entire hand had turned a collage of reds, blues, and yellows, all swirling together across his skin. She gently held his hand in her own, flinching slightly as she felt hard plastic rather than flesh, the light reflecting off the glossy material. She squeezed his palm gently, but there was no give. It was as if his whole hand had turned into plastic.

"Izuku…" She murmured, both in fear and in wonder. "What happened?"

Izuku's tears had finally started to fall as he gasped between sobs. "I-I was just p-playing with All M-Might, and then-and then my hand got all t-tingly, and -th-there was a l-light, and now All Might's goonnnne!"

Inko pulled Izuku into a hug as his crying grew worse, forcing down her own panic as realization slowly started to form in her mind. "Izuku… Izuku, it's okay, sweetheart." She rubbed comforting circles on his back as he held onto her, sobbing into her chest. "Please calm down, Izuku. I think I know what happened."

Izuku pulled back just enough to look into her eyes. "Y-You do?" he hiccuped.

Inko smiled gently as she sat down on the kitchen floor, Izuku instantly clambering into her lap. "I think so, sweetie. Now, does your hand hurt? Can you move it at all?"

Izuku sniffed some more, but looked down at his miscolored hand. He flexed his fingers hesitantly, causing a small clacking sound as the plastic rubbed against itself. "I-It doesn't hurt." He murmured.

Inko let out a breath she hadn't realized she'd been holding. "Good. That's good. Okay… Izuku?" She waited for him to look up at her before smiling brightly. "Sweetie, I think you just got your Quirk."

Just as she'd been hoping, Izuku's eyes grew incredibly wide, his little mouth popping open. "I...I did?"

Inko chuckled at his starstruck look. "I think so. You said you felt a tingling feeling in your hand?"

Izuku nodded slowly, his tears lessening. "Y-Yeah. Like, when I sleep on it? All numb and needley? It was like that, but… different."

Inko nodded with him, humming. "Okay… can you try this for me? Think really, really hard about that feeling. Try to make it happen again."

Izuku frowned slightly, but gave her another nod. "Okay, Mommy." He then stared very intently at his plastic hand, his brow pinching together as he brought up all the focus a four-year-old could muster.

Inko watched with bated breath, hoping Izuku could figure out just a little of his Quirk before they had to seek out professional help. She clasped her hands behind his back, holding him as he focused.

After a few minutes, Izuku let out a little groan of discontent. "I can feel something, but nothing's happening!"

Inko gave him a gentle smile. "It's okay, Izu. Don't feel you have to force it, sweetie. Maybe the doctor can help when they confirm you have a Quirk."

Izuku just pouted stubbornly. "But I can do it!" He shouted. "I just have to try harder and not give up. Like All Might!" He closed his eyes, focusing hard.

Inko sighed at his stubbornness. "Izuku, you…" She trailed off, her eyes widening as there was another flash. She looked down sharply, just in time to see Izuku's hand glow with green light. It seemed to bend and twist as the light grew brighter, until she could make out a familiar shape.

The light died down in under a second, and Izuku's eyes popped open in surprise. He grinned brightly. "Mommy, look! All Might's back!"

Inko nodded faintly. Yes, the All Might action figure had indeed returned, clutched tightly in the once-again-flesh hand of her son. She shook her shock off quickly, hugging Izuku tightly. "Good job, Izuku!" Still holding him proudly in her arms, Inko stood up and quickly snatched her phone off the countertop. It was already ringing as she squeezed Izuku into a crushing hug, making him giggle.

With a click, someone picked up. Inko briefly heard the indignant squeak of an upset child, before a woman's voice came on the line. "Hey, just a second, brat, someone's calling me… Hello? Inko, that you?"

"Mitsuki!" Inko answered back, grinning like no tomorrow. "Mitsuki, you won't believe what just happened!"

Three hours and one doctor's visit later found the Midoriya's in the home of the Bakugo family. The door had just barely opened before Izuku, now clad in blue shorts and his favorite yellow All-Might t-shirt, gave a hurried hello to 'Auntie Mitsi' and rushed down the hall toward his best friend's room, their mothers' laughter following him the whole way. He started beating on the door like his life depended on it.

"Kacchan! Kacchan! Lemme in lemme in lemme in!"

The door swung open without warning, causing Izuku to fall flat on his face with a yelp. A bark of laughter made him look up, seeing his friend Katsuki smirking at him with his hand still on the doorknob, dressed in long pants and a black sleeveless shirt.

Izuku pouted up at him. "Kacchan, that's not nice!"

Katsuki, or Kacchan, as Izuku chose to call him, just snorted. "Deal with it, Deku."

Izuku's pout deepened at the nickname, but was quickly wiped away as he jumped to his feet. "Kacchan! Guess what, Guess what!"

Katsuki crossed his arms, pretending to look thoughtful. "Hmm, I guess…" He then gave Izuku a flat stare. "You got your Quirk?"

Izuku stopped bouncing in place, his face going slack. "Wha-? How did-?"

"My mom already told me," Katsuki stated with a smug grin.

Izuku slumped heavily, his enthusiasm replaced with disappointment. "Aww… I wanted to surprise you…"

Katsuki snickered at Izuku's downtrodden expression. "Tough." His grin turned less smug as he looked Izuku up and down, a little thoughtful. "So…" He drawled, trying to sound like he wasn't interested. "What is it?"

Izuku's eyes sparkled in an instant. "You really want to know?"

Katsuki fixed him with a flat stare. "I wouldn't have asked if I didn't want to know, Deku. I mean, obviously, it can't be as awesome as my Quirk…" As if to prove his words, Katsuki held up his palm, a series of crackles and pops flickering across his palm, making Izuku go starry-eyed as always. Katsuki smirked. "But-"

"Brat, you better not be blowing stuff up in the house again!"

Both boys jumped at the sudden shout. Katsuki scowled as he marched to the door, sticking his head out into the hall as he shouted, "I'm not, Mom!"He slammed the door shut, muffling whatever his mother yelled back. He turned back to Izuku, carrying on like nothing happened. "So, yeah, it can't be as awesome as my Quirk, but… is it at least kinda cool?"

Izuku's whole face lit up. "It's so cool! I can combine with stuff!"

Katsuki blinked at him, tilting his head. "Combine? The heck does that mean?"

Izuku just kept smiling, undeterred. "Watch!" Reaching into his back pocket, Izuku pulled out his All Might action figure. Katsuki watched, curious, as Izuku's face scrunched up as he stared intently at the toy. There were a few seconds of nothing, making Katsuki impatient. But right when he was about to yell at Izuku to do something, Katsuki flinched back as Izuku's hand started glowing with green light.

Katsuki watched, mesmerized, as the glow encompassed the action figure. Once the toy and Izuku's arm seemed to glow equally as bright, the toy seemed to sink into Izuku's hand, the two merging. Once the glow died down, Izuku's hand had turned the same melted colors the action figure had once been, stopping just below his wrist.

"Whoa…" Katsuki couldn't help but utter.

Izuku took his friend's apparent amazement as a cue to begin bouncing in place again. "See? I told you! Cool!"

Katsuki nodded dimly, staring as Izuku flexed his hand. "Okay… yeah, it is." He then looked back up to meet Izuku's eyes. "But wasn't that your favorite toy?"

"Oh, I can bring it back. See?" Sure enough, with just another green glow, Izuku's arm was back to normal and the All Might action figure was right back where it had been, good as new.

Katsuki let out a small laugh. "Cool… can you only do it with plastic?"

Izuku blinked at him, so wrapped up in the excitement of having finally gotten his quirk that he hadn't thought that far ahead yet. "Um… I don't know," He admitted, shrugging his shoulders.

Katsuki hummed a little, then started looking around his room. He zeroed in on his toy chest quickly running over and digging through it. Izuku followed him, looking over his shoulder to try and see what Katsuki was looking for.

His answer came when Katsuki pulled out a deflated basketball, grinning widely. "Want to find out?"

As it turned out, Izuku's quirk was not limited to plastic. Actually, it didn't seem like there was any limit to what he could combine with. Over and over, Katsuki handed over more and more items from around his room for Izuku to try combining with, both of them growing more and more excited with every success. The basketball, a bedside lamp, more action figures, Katsuki's pillow; Izuku could merge with all of them, his arms becoming whatever material he absorbed.

Slowly, the two worked out a bit more about how Izuku's Quirk worked as they sat in the middle of the room experimenting. If he merged with something for more than a few minutes, he started to get a headache. He could merge with more than one thing at a time, but the headache grew worse faster when he did. The bigger something was, the farther up his arms he could change (absorbing the basketball had stretched rubber nearly up to his elbow, while the jacks Katsuki had pulled out of his pocket had barely covered his palm). Whatever part of Izuku's body was merged was harder for him to feel, as he learned when Katsuki tapped on his rubber arm and he found he couldn't feel it.

Then, as he tapped the knuckles of his bouncy-ball infused knuckles together, Izuku had a thought. "Oh! What if I merged with something metal? I bet I could punch really hard then. Like All Might!"

Katsuki, who had been having a surprising amount of fun watching his friend combine with his toys and bring them back unscathed, gave a fearsome grin. "Now you're thinking like a hero!" He ran back to his toy chest, pulling out an aluminum baseball bat. He ran back to Izuku, excited. "Give this a tr-whoa!"

Izuku looked up as he started bringing the bouncy balls out of his skin. Katsuki had stepped on one of the baseballs they had left lying around and tripped. Izuku threw his hands out reflexively to catch him. "Kacchan! I got-"

Izuku didn't notice that his hands were still glowing as he grabbed Katsuki by the arm. Not until a bright green flash filled the entire room.

Red eyes blinked open as he fell onto the carpet, the green glow fading around him.

What… just happened?

He pushed himself, looking around the room in confusion.

Where… where did Kacchan go? What the heck happened to Deku?

He looked down at his hands, turning them face up. Something felt… off.

I was falling. But I caught him? But then… where…?

He stood up on shaky legs, still looking around the room as if his missing friends would just appear. He frowned.

But… I'm not missing. I'm standing right here.

He started walking towards the door. Maybe one of his moms would know what was going on.

Wait… moms? I only have one mom!

...don't I?

Out the corner of his eye, something moved. He turned sharply to face… Katsuki's mirror.

He stared at his reflection for a moment, blinking in confusion. Then his eyes widened. He suddenly realized what felt off.

"Oh… oops…"

"Yeah, I remember when Katsuki first used his Quirk. Poor brat was so sad that he blew up his favorite blanket."

Inko covered her mouth, trying not to laugh. "Oh, dear. I'm glad Izuku was able to bring his toy back out. I don't even want to think about the fit he'd of had."

Mitsuki snorted as she pulled a bucket of ice cream out of the freezer. "Couldn't have been any worse than my brat. The windows were rattling with how much he bawled."

Inko rolled her eyes at her friend's flippant words. "Mitsu…" She scolded lightly.

Mitsuki waved her off. "Oh, the brat can survive a little embarrassment. Are we all ready here?"

Inko nodded as she looked over the living room, setting down a few plates around the freshly baked cake, the words 'Congrats Izuku!' written across the top in chocolate icing. "I think so. Oh, thank you for helping me with this, Mitsuki."

"Oh, don't even," Mitsuki laughed. "Kid gets his Quirk, he deserves a party. You finish setting up, I'll go get the brats."

Mitsuke smirked lightly when she heard Inko's exasperated sigh. She loved her childhood friend, but Inko was just too easy to rile up sometimes.

She made her way down the hall, knocking on Katsuki's door. "Boys? Cake's ready."

The lack of an immediate excited shout was an instant red flag.

Mitsuki frowned as she knocked again. "Izuku? Katsuki? What, you two fall asleep?" With a further lack of response, Mitsuki's mind went to the most reasonable explanation. Gritting her teeth, she yelled as she shoved open the door. "Okay, Katsuki, what did you break this-"

Her words died in her throat as she looked down at the boy in front of her. The only boy in front of her.

"...Mom?"

Mitsuki's mouth hung open, her eyes blowing wide.

"Mom? I think I did something wrong."

She worked her mouth, her attempts at speech coming out as little more than weak gasps.

"Mom… are you okay? You look freaked."

She finally managed to find her voice, though her first word sounded suspiciously like a squeak. "I'm… fine… k-kiddo. Just, uh… One second?" She held up a single finger in question, before turning back down the hall and shouted. "Inko?! I think we have a problem!"

The boy flinched at her sudden yell, and Mitsuki would worry about feeling bad just as soon as she stopped freaking out!

"Mitsuki?" Inko came rushing down the hall, looking worried. "What's wrong?"

Mitsuki just opened the door wider, pointing at the boy without looking. Inko looked in, clasping her hands over her mouth as she gasped. Mitsuki couldn't help but agree.

The boy before them had large red eyes flecked with green and green spiky hair, spots of blonde peppered throughout as it curled at the side. He had faint freckles running along his smooth cheeks, his eyebrows sharp. The questions the two mother's had for where he came from were slowly answered when they noticed that he wore Izuku's shorts over Katsuki's pants, and Katsuki's sleeveless shirt over Izuku's All-Might tee.

The boy seemed to shrink into himself as the women just stared at him. "Am I in trouble?"

Inko sucked in a harsh breath. Her lingering doubts were wiped away by the boy's voice… or rather, his voices. When the boy spoke, it was as if Izuku and Katsuki were speaking in tandem. She turned to Mitsuki, seeing the same realization in the blonde's eyes.

"I thought Izuku's Quirk just let him combine with objects?" Mitsuki asked quietly.

"I thought that's all it was," Inko breathed. She swallowed as she looked back down at the boy. "I-Izuku?" She asked hesitantly.

The boy cringed slightly under her gaze, but managed a small smile as he waved. "H-Hi, Mommy."

"Katsuki?" Mitsuki then asked, her voice a little stronger.

The boy cringed again, even harder, but managed a slightly bigger smile. "H-Hey, Mom."

Out the corner of her eye, Mitsuki saw Inko wobble. Her head snapped to the side in an instant. "Inko, don't you dare faint on me!"

Inko stiffened, but still looked woozy. "Trying not to, Mitsu." She slowly sunk to the ground, her eyes never leaving the boy… her son.

Mitsuki huffed, but followed Inko to the ground. Apparently, she'd have to take the reigns here. She sat haphazardly on the carpet, just now noticing her son's toys scattered all around the room, mostly around the boy in question. "Okay, kiddo. Or, uh… kiddos?" She gave her head a small shake, plowing ahead. "What happened? What did you… two… do?"

"Um…" The boy looked between the two women, wringing his hands together. "Izuku and Katsuki were testing out Izuku's Quirk, when Katsuki tripped. Izuku caught him, there was a flash, and then…" The boy shrugged helplessly. "I was here."

Mitsuki frowned. "You were here? Aren't you Katsuki and Izuku?"

The boy's brow furrowed. "Um… kinda? I'm them, but I'm also me. I'm… both?"

"Your name…"

Both Mitsuki and the boy turned at the sound of Inko's faint voice. She faltered slightly under their attention, but then bit her lip. "If you're both of them… what do we call you?"

The boy blinked. "Huh… I didn't think about that." He rubbed the back of his head as he thought. "I'm made of Izuku and Katsuki. So… maybe if I put both names together? Like… Izuki?" He frowned, then shook his head. "No, that sounds like a girl's name. Maybe… Kat...zuku?" He thought for a moment, then a wide grin spread over his lips. "Yeah… yeah! I'm Katzuku!" The newly dubbed Katzuku crossed his arms proudly, giving a toothy grin.

Inko and Mitsuki shared a look. "Well… apparently our kids just… fused themselves together. Did you think this was how your day was gonna go?" Mitsuki asked with a weak grin.

Inko glowered at her friend's attempt at a joke. "Mitsu, could you please not?"

Mitsuki rolled her eyes. "Oh, fine. Okay… Katzuku."

Katzuku turned to her with a smile. "Yeah, Mom?"

Mitsuki tilted her head slightly. Now that she'd calmed down, she couldn't decide which was weirder: hearing Izuku's voice call her 'Mom', or hearing Katsuki's voice sounding polite. "Just… Do you feel… okay?"

Katzuku frowned at her. "Um… yeah?" He looked down at himself in question. "Nothing hurts, if that's what you mean."

Mitsuki nodded, and Inko let out a breath of relief. "'Kay… good. Now… uh… don't take this the wrong way, kiddo… But do you think you could… y'know…" She pointed both her index fingers at him, then moved them apart. "Split?"

Katzuku blinked, tilting his head to the side. "Um… I think so." He looked between the two women. "Do you want me to?"

Inko and Mitsuki shared another look. Inko bit her lip, but then gave Katzuku a warm smile. "If you could. I'm sorry, Katzuku, but… this is a bit much. I think we need to speak to our boys… separate… before moving forward. Is that okay?"

In an instant, Katzuku gave them both a beaming smile. "Yeah, It's okay! This is weird for me too!" He giggled, making Inko and Mitsuki smile. Then he looked thoughtful. "Can I do just two things first?"

Another look was shared between the mothers. "What do you want to do?"

Katzuku grinned, and Mitsuki went on edge due to how much of Katsuki she saw in that smile. "Well, first I want to see if I can still do this." Before either mother could stop him, Katzuku held his palms up and focused on them. A familiar crackling and popping sound filled the air as tiny firecracker sized explosions sprung up across his palms. Though, rather then the simple lights Katsuki's explosions made, Katzuku's all flashed green. "Cool…" He muttered to himself.

Mitsuki felt her eye twitch a little. "Katsuki…" She growled warningly.

Despite the slip of the wrong name, Katzuku looked up to meet her gaze. He smiled sheepishly. "Right… No explosions in the house. Sorry, Mom."

Mitsuki let out a small breath, letting it go on the sheer fact she got an actual apology for once. Inko giggled lightly at her clear annoyance, before turning back to Katzuku. "And… the other thing, sweetie?"

Katzuku blinked, then smiled. "Oh, right!" Without warning, he suddenly jumped into Inko's lap.

Inko squeaked in surprise, only to freeze when she felt his small, surprisingly strong arms wrap around her.

"Bye, Mommy."

Inko sucked in a small breath. "G-Goodbye, Katzuku" She murmured into his air, hugging him back.

Before she could say anything else, Katzuku had already launched himself at Mitsuki, wrapping his arms around her neck. "See you, Mom."

Mitsuki had the same dazed look Inko was sure she had, but managed a small grin as she squeezed him. "See ya later, squirt."

Katzuku backed up a step, giving them both one last smile. Then he closed his eyes, focusing.

Inko and Mitsuki watched as Katzuku started to glow. There was little to no build up, his whole body being engulfed in a bright green light, so intense that the two mothers had to squint in order to still see him. For one brief moment, they could see his body split right down the middle…

And then the light was gone, and Izuku and Katsuki were falling away from each other, yelping in surprise. Izuku's body kept glowing for a few seconds before fading back to normal.

The two boys slowly sat up, blinking at each other.

"...That was… weird." Katsuki finally said.

"Really weird." Izuku nodded in agreement. Then he gave Katsuki a concerned look "Are you okay, Kacchan?"

Katsuki scowled at him. "Of course I'm okay, Deku! You really think you could hurt-ugh!"

His would-be insult was cut short when the little blond found himself pulled into a bone-breaking hug by his mother.

"Brat, you ever scare me like that again, I'm going to ground you for life, you hear me!?" Mitsuki near yelled as she crushed her son against her chest.

"Mom, get off me! It was all Deku's… urk!... Mom… Mom, you're squishing me…"

Izuku wasn't much better off, his own mother holding him in a death grip as she took deep ragged breaths.

"Mommy?" He asked softly, trying to wriggle his way out enough to see her face. "Mommy, what's wrong?"

Inko had to take a few more deep breaths before she was able to speak. "Izuku…" Her voice was low and scratchy, heavy with emotion. "Izuku, sweetie, you have no idea how much you just scared me." She carefully pulled away from him so he could see her stern gaze. "Promise me that you'll never do that again."

Izuku's face fell, tears forming in the corner of his eyes. "Never?"

Inko held her stern face for a moment, before Izuku's broken-hearted look made her relent, if only slightly. "Just… at least not unless I'm there to watch you. Okay?"

Izuku sniffed, but gave a firm nod. "Okay."

Inko smiled at him. She kissed his forehead, then pulled him in for another hug.

"That goes double for you, Katsuki!" Mitsuki said as she continued to squeeze her son. "I don't care how 'cool' you think it is, I better not hear about you making Izuku use his Quirk like that without your Auntie Inko's say so. Got it, brat!?"

"I...I got it!" Katsuki growled back, though it sounded more like a whimper as he struggled against his mother's ironclad hug. "Just… lemme go already!"

Inko chuckled slightly at her unofficial sister and nephew, just enjoying the fact that her son was back in her arms, safe and okay.

"...Hey, Mommy?"

Inko looked down slightly at the sound of her son's voice. "What is it Izuku?"

"I think I know what I want to name my Quirk now."

Inko pulled back just enough to meet his eyes. "Oh? And what's that?"

The smile Izuku gave her was so bright it would warm her heart for years to come. "I'm going to call it… Fusion!"

A/n: So this is basically a 'Izuku hasa Quirk' AU, with that quirk being a mashup of Kevin Levin's power from Ben 10, slightly modified, and the various fusion abilities from Dragonball and Steven Universe.

Why did I make this? Well, the conversation went something like this:

Plot Bunny: Hey. You.

Me: Huh? Who are you?

PB: I'm a Plot Bunny. You're going to write a thing.

Me: ...but I don't want to write a thing. I'm supposed to be writing the next chapter of LiLaL.

PB: Don't care. You're writing a thing.

Me: But I…

PB: WRITE THE THING!

So… this is that thing. Not sure how often it'll update, since LiLaL takes priority for the immediate future, but if people show enough interest, who knows? I'll admit, this was fun to write, and I wouldn't mind seeing how far I can take this premise. I can see it being a lot of fun in the future.

See you all… well, whenever!