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2024-09-24
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2025-08-15
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36/?
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Different Worlds- MHA x KNY

Summary:

Falling into the Infinity fortress was the last thing Tanjirou could recall before waking up in a strange environment, which he and his friends were pulled into at U.A. High. Navigating a new world with the hopes of defeating the Demon King and finding their ticket back home. Despite the peaceful moments and piecing together of questions and answers, things got a lot more complicated and harder on both sides.

Or Tanjirou and the Demon Slayer Corps end up stranded in the world of MHA. Mystery and lots of chaos ensue!

Characters belong to the Creator of MHA (Kohei Horikoshi) and KNY (Koyoharu Gotouge)

1-14(Rewritten)
15-29(OG- rewriting in progress)

Notes:

Hey there! Thanks for stopping by! This is my first attempt at fanfiction and a crossover. Something I picked up for fun, as a hobby, and to grow in writing even when burnouts creep in, and also because I might have read lots of MHA and KNY crossovers till I felt like doing mine, just different. Hopefully this fic makes someone's day, whether laughing or smiling. so wish me luck and enjoy!

(See the end of the work for more notes.)

Chapter 1: From Infinity to U.A

Summary:

What if a random portal appeared just before the battle in the Infinity Castle could take place? Meanwhile, things go smoothly at U.A. unaware of the phenomenon that could cause a lot of changes with their new arrivals.

Notes:

(See the end of the chapter for notes.)

Chapter Text

The magnificent yet tragic explosion struck the Ubuyashiki mansion in the chill winter night. The time had come. The final battle between the Demon Slayers and Demons was about to take place. Kasugai crows cawed in the air, alerting their owners of the breach in the Ubuyashiki household.

The sight ahead left everyone stunned, uneasy, and breathless with fear as they quickened their pace to where the explosion occurred. Their heads beaded with sweat and various expressions that etched with dread and dwindling hope as the word hurry chanted in their thoughts like a mantra.

The scent of burning flesh invaded Tanjirou's nostrils, forcing him to skid to a stop alongside the Water Hashira. Both stood wide-eyed, the sheer scale of the blast sending a forceful wind that flapped their haoris backwards.

Oh no... The Master...His Family.

Tanjirou's hand visibly trembled, looking on. Forcefully snapping himself out of his thoughts, he continued with Tomioka towards the site.

At the site of the explosion, Gyomei frowned at Muzan's regeneration speed. Even after Tamayo's ploy to weaken the Demon King, Muzan appeared completely unfazed. He was truly terrifying. There was no other option. He had to stall until the sunrise—and pray the rest of the corps arrived as well to take him down.

Swiftly, Gyomei moved, tightening his grip on his weapon and deflecting Muzan's blood demon art with ease. Muzan roared, shoving his fingers deeper into Tamayo's skull for her to release him, but the demon lady was unrelenting. This wasn't how it was supposed to go for him. He wouldn't let it happen.

Unfortunately for him, the corps began to assemble.

"YOU BITCH! WHAT THE FUCK DID YOU DO TO THE MASTER!?" Shinazugawa Sanemi shouted angrily, coming into view. Eyes burning with unfiltered rage as he stared down at the Demon King. Gyomei let out a satisfied hum at the sight of the pillars gathering.

"Master!" Iguro and Mitsuri arrived seemingly at the same time, hands on the hilt of the sword. They froze, taking in the scene before them, and the Stone Hashira used this chance to shout out.

"IT'S MUZAN! KIBUTSUJI MUZAN! HE WON'T DIE EVEN IF YOU CUT HIS HEAD OFF."

He was right there. In the midst of the chaos. Breathing the same air as them. The many unforeseen and depressing deaths. Bloody wails, woes, and harms that rose just from this thing alone, the reason for the many lives lost.

He ruined their lives!

The Progenitor of Demons.

The Demon King.

Slit red eyes scanned the faces of the Hashiras before landing on dark red ones with white pupils. A sharp breath was taken, Tanjirou's kind and worried eyes suddenly hardened with his target locked in sight, and veins popped from the corners of his head. He drew his sword quickly and cried out.

"MUZAN!"

Like that, all hell broke loose.

Mist breathing, Fourth form.

Insect breathing, butterfly dance.

Serpent breathing, first form.

Love breathing, Fifth form.

Water breathing, third form

Wind breathing, Seventh form.

Hinokami Kagura, Sunflower Lance...

Muzan smirked malevolently, like it all went according to his plan. The strum of a biwa caught everyone puzzled, transforming to astounded and horrified looks. Below them were traps that led to the Infinity Castle. Every member of the corps had gotten caught in it.

As they fell, Muzan wore a crazy grin, staring down at them.

"You seriously thought you all were going to corner me in hell. You are all going to hell now. You pathetic Demon Slayers, I'm slaughtering you all tonight!" Muzan proclaimed, watching Tanjirou land on a platform, but another strum of the biwa caused him to continue falling again.

Tanjiro gritted his teeth. "You are the one going to hell, Muzan! I will defeat you for sure!"

"Come and get me if you can, Kamado Tanjirou!" Muzan jeered.

A white void popped up beneath Tanjirou, his eyebrows creased as well as Muzan's.

This can't be Nakime's doing.

Cries from demons broke out from the castle on getting swallowed by the unfamiliar void. Tanjirou's eyes dilated on seeing Tomioka get enveloped by the space too. He bit his lip, his mind racing, trying to process what's happening.

What is that?

Is everyone else—

His throat ran dry, holding his breath as he fell into the void.

They didn't have a clue, did they? What portal they descended into. The grips on their swords were held firmly, and their faces were ready. They plunge, awaiting their fate.

Unbeknownst to them, A new world awaits.


White clouds drifted lazily in the blue sky of this new world. At U.A.'s cafeteria, a bubbly voice called out repeatedly.

"Deku...Earth to Deku."

"Oh, hey, Uraraka!" On his seat, Midoriya snapped out of his thoughts, turning to his friend, who stood with a food tray in hand.

"You were spacing out. Something wrong?" Uraraka nudged with her elbow, setting her meal on the table before sliding into the seat next to him.

"Oh, I was just thinking of what Mr. Aizawa has in store for us later today." Midoriya replied, finally taking a bite from his lunch. "You know, change into our P.E. uniforms and head over to the field." He continued with his mouth full.

"You shouldn't talk with your mouth full, Midoriya." Another familiar voice joined in the conversation.

The two looked up, seeing Iida and Todoroki with their respective food trays. They took the empty seats across from then and set down their lunches opposite the two. Uraraka chuckled softly at the stuffed cheeks of the boy next to her, whose cheeks flushed a pink hue.

Midoriya swallowed, chuckling a bit. "My bad, thanks for the heads-up, Iida."

"Don't mention it. As the class rep, I, too, have to ensure the well-being of my classmates and friends." Iida nods, pushing his glasses back. "That said, I have the same assumptions as you. The teachers have a meeting this afternoon, so the sudden change of events is concerning."

"I wonder what changed." Uraraka hummed.

Todoroki wasn't a person of many words. Yet, he believed that shouldn't stop him from interacting with his friends. He'd grown closer to his classmates ever since the training camp. He ate from his soba, staring at it quietly before saying.

"It might not be different from the other trainings we've had, but it's Mr. Aizawa we are talking about." The others nodded in agreement as they transitioned to other topics.

Meanwhile, at another table, Kirishima brings up his theory.

"You think Mr. Aizawa's in a bad mood? I don't want to believe it, but..."

"You might be right. He did look exhausted today." Kaminari adds, trying to mimic his teacher's signature look.

"Idiot. He always looks like that." Jirou replied, making Kaminari grimace.

"Yeah, but it could just be him waiting to torture us again with relentless training exercises." Sero shivered while patting Kaminari's back sympathetically.

"I bet whatever he has for us is going to be related to our end-of-the-term test scores. Seems pretty likely if you'd ask me." They blinked Mineta's way.

"What?" Mineta raised a brow.

"Dude, are you okay?"

"Mineta, who hurt you?"

"Sounds way off character."

"You aren't trying to jinx us. Are you?"

"Oh, come on! I can be insightful too, you know. I'm just stating facts. I don't like this change in our schedule one bit!" Mineta let out an exasperated sigh, flailing his arms in the air.

"There's our Mineta!" Sero grinned.

Mineta snorts, "Please, it's because I mentioned test scores—Woah! I'm delicate here!"

He shrieks from Sero and Kaminari smacking his head lightly. Bakugo, seated between Kirishima and Kaminari with his arms crossed, albeit begrudgingly, gave an irritated side-eye at the three making a ruckus.

"Will you bastards shut the hell up? I'm trying to eat here."

"Wait, you didn't bat an eye at us earlier. So does this mean you care about how we feel?"

"Tch. Shut up and eat your meal, Sparky. I'm not the one worried about getting 20th place." Bakugou scoffed.

"Had to rub it in, huh?" Kaminari slouched again with Sero comforting him.

Minutes later, the bell rang, signaling the end of lunch break. The hallways buzzed with students exiting the cafeteria with hurried steps to their various classes and respective period subjects as the day went on. After a few periods, Class 1-A left for the changing room to put on their P.E. outfits. Once finished, they made their way to the P.E. training grounds.

Aizawa remained next to Midnight, scrutinizing his students with a lazy eye. Seeing as they all gathered, he began.

"Right, let's get this over with. I suppose you are all wondering why there was a sudden change in today's plans. The Principal adjourned the meeting for later. Now, this is just a P.E. session. It will not be recorded as part of your scores at the end of the term."

Relieved sighs escaped their lips, but he didn't let up. "However, Those scoring bottom last will be cleaning the dorms and classroom for the rest of the month."

He is definitely in a bad mood. The class thought as cold sweat dripped from their foreheads. Tsuyu raised her hand.

"Yes, Asui?" Aizawa acknowledged, shifting his gaze to her.

"Not to sound blunt, but is there a reason why Miss Midnight is here, ribbit?" Asui asked.

"Yes. She is here to supervise and evaluate your performance." The man answered, surprisingly holding his yellow sleeping bag, which wasn't noticed till now. He continued walking back to the school. "I'm off to handle some paperwork."

Paperwork, right...

He's not even hiding it.

"Alright, everyone! This is a relay race containing various obstacles and hero rescue scenarios. You will be split into five teams. Quirks are allowed, but remember, no getting in the opponents way." Midnight informed them, cracking her whip in the air for dramatic effect, making them flinch.

Murmurs and whispers of excitement followed. This was a new sort of training, and eager as they were, everyone was determined to give their all to this task.

The teams were as follows:

Group 1: Todoroki, Uraraka, Asui, and Kaminari.

Group 2: Mineta, Iida, Kirishima, and Hagakure.

Group 3: Midoriya, Jirou, Koda, and Sato.

Group 4: Bakugou, Aoyama, Ojiro, and Yaoyorozu.

Group 5: Tokoyami, Ashido, Sero, and Shoji.

"You've got five minutes to decide your starting and follow-up positions." Midnight adds, watching as each group started huddling together. A small, curious smile made its way to her face. She recalled when their homeroom teacher allowed her to supervise when she asked him about it. Together, they brainstormed what teams to put together. Heroes won't necessarily be put in situations that would suit their group, quirk, or abilities. So they have to improvise.

Five minutes were up, and the first leg came towards the line. Asui, Mineta, Sato, Aoyama, and Sero were in position in their respective lanes.

"On your mark... Set....GO!!" Midnight cracked her whip in the air.


"Well, what do we have here? Class 1-A is having a training session, flaunting their quirks as usual." Monoma sneered, looking through the window in Class 1-B.

It was a free period, and the students of Class 1-B watched their sister class demolish and clear through the obstacles while trying to rescue as many displaced dummies as they could. Wide eyes peeked through windows, silently cheering and placing bets on who they thought would come out on top.

"Looks real fun if you ask me. It's getting me excited already." Tokage grinned, looking on.

"Kirishima's on a roll! His quirk may not help much in running, but he is demolishing those obstacles." Tetsutetsu clenched his fist, watching the red hair continue unfazed despite the smacking pillars.

"What!? Nothing but a bunch of—Ack!" Monoma quickly got cut off by a swift chop to his neck by his class representative, Kendo.

"Monoma, Kan-sensei wants to see us." She said, dragging him out of the class.

Once outside the classroom, Monoma winced, favoring his neck. That hit wasn't enough to send him unconscious as always, but it still hurt.

"Have your chops gotten firmer? Seriously, you have to stop that. You might break my neck one day." Monoma grumbled, glancing at her.

"I'll stop when you stop persecuting our sister class." Kendo replied, glancing back with a smile. Her brows furrowed, wondering why he stopped walking with her. Slowly, she looked forward in the hall.

Three boys lay sprawled on the ground with traditional Japanese garbs. A sort of uniform having white belts and hakama pants. The first boy they looked over had boarhide covering his facial features. He lay half naked next to the blonde boy who wore a yellow haori with triangular white patterns on it. The last one was wearing a green and black checkered pattern haori, with a visible scar on his forehead.

"Hey! Are you okay? Can you hear me?" Monoma spoke with urgency as he and Kendo rushed to the side of the unconscious boys. He knelt next to Inosuke, checking his pulse, and breathed a sigh of relief.

"They're fine. Just unconscious. No signs of wounds on them either." Kendo's shoulders fell after examining them. She turned to face her classmate. "I've never seen these guys before at U.A."

Monoma lifted a brow, sizing up the three before snapping up to face Kendo.

"Yeah..." he drawled, eyes lingering on their swords. "Same. What actually happened here? And who are they?"

Kendo mused internally, a hand on her chin before glancing at him. "Still, let's get them to recovery, girl."

Monoma hesitated at first but agreed shortly. He grabbed the blonde-haired slayer and boar head.

"These guys are heavy, especially the boar head." Monoma grunts. He felt like a clumsy ballerina while Kendo tossed the other's arm over her shoulder. The two students exchanged a nod before making their way to the clinic.

Recovery girl was nowhere in sight in the office. The scent of antiseptic invaded their senses, bringing them back to reality. Carefully, the two students set the boys on available beds, with Kendo suggesting to go look for the youthful hero.

"And I'll stay here to watch these guys until you get back." Monoma agrees with a subtle nod. With that, Kendo leaves the office. After a while, she spots the lady in a heartfelt discussion with the two homeroom teachers of the first-year hero classes.

The corners of her eyes crinkled with a small turn up of her lips.

Bingo.


#Preview

"Could they be villains who invaded the school? But that's impossible given the security record U.A. has..." Kendo mused in a corner. She rubbed her temples with an exasperated sigh. "Well, except for that time when reporters tried to breach the school on our first week."

"Or...they could be new students. Principal Nezu decided to introduce to the hero course...maybe 1-B."

Monoma immediately brought his hands up at her deadpan. He continued, "You never know, I might be right."

"Sure, Monoma. Sure...." Kendo rolled her eyes playfully. "Next, Chapter: Escape With Misconceptions."

 

Notes:

Also, as a heads-up for upcoming chapters, they may differ slightly. I wrote this fic a year ago, so my writing has improved since then. As i work on providing new chapters, I might update the current ones. I also made a few tweaks to align with it since I wasn't fully satisfied with how I started the fic. Wish me all the best!