Actions

Work Header

Rating:
Archive Warning:
Category:
Fandom:
Relationships:
Characters:
Additional Tags:
Language:
English
Stats:
Published:
2026-02-19
Updated:
2026-05-14
Words:
29,597
Chapters:
7/?
Comments:
13
Kudos:
64
Bookmarks:
18
Hits:
1,520

Soulstice

Summary:

The way his second year of high school started wasn’t something Katsuki could have anticipated—with one of his bullying muses from middle school, Y/n, joining Class 2-A.

Now he has to face her again, after what happened five years ago; after what he had said to her, did to her. Them discovering that they're one another's other half not only throws a massive wrench into things, but also triggers one of them to Reassign.

Forced into a soul bond with the last person one would expect, or wanted, and suddenly becoming an Omega..

Absolutely spells disaster.

Notes:

𝐒𝐨𝐮𝐥𝐬𝐭𝐢𝐜𝐞
(Noun)
the moment you realize you've become a different person, making a shift in your inner landscape

𝐖𝐡𝐚𝐭'𝐬 "𝐑𝐞𝐚𝐬𝐬𝐢𝐠𝐧𝐢𝐧𝐠"? (click to expand)

A medical phenomenon in which one's secondary gender can (seemingly) randomly change. Nobody knows why or how this happens, what group of people gets Reassigned more than another, nor what can/will trigger it.

A scientist discovered that individuals who Reassigned had a different blood type that then coincides with the new secondary gender they've become. For example, if someone is first a Beta and Reassigns to an Alpha, their new blood type is A. Depending on what someone is being Reassigned as, symptoms can vary in intensity. Such as becoming overly sensitive to scents when you weren't previously, hot flashes and fever, and an overall feeling of being unwell while the changes are being undergone.

Reasons for any of this are still unknown.

𝐏𝐞𝐫𝐬𝐢𝐬𝐭𝐞𝐧𝐭 𝐍𝐨𝐭𝐞𝐬 ↻ (click to expand)

— Primary thing to mention, Mineta doesn’t exist in this universe. There’s magically an empty desk for you, and we’re not going to question it, got it? Good
— The first few chapters use the last few episodes/manga chapters as reference, so there's canon dialogue included (paraphrased more or less) in ch1-2.
— I kept it pretty close to canon (while sprinkling my own stuff in here and there for the in-betweens, ofc) as much as i could, but I have omitted a handful of various things in order to prioritize this story’s progression (also because I just don’t feel like adding/writing them ✨)
— Both “Y/n” and “F/n” is used, but mostly "Y/n".
— The fic is written in third person! Meaning she/her is used for reader instead of you/your.
— Tenses aren't consistent throughout the entirety of a chapter. I switch between present and past; primarily present for paragraphs containing dialogue, and past for everything else. Sometimes they're mixed, but not crazy often. Or I'll just straight up make a non-dialogue sentence/paragraph in present tense anyways; it really just depends on what I feel is fitting for the specific scene..
— Y/n is basically coming into this whole thing unaware of 90% of what happened (basically everything in the series) since she’s been away from the city. So to “honor” that, I want to keep the writing somewhat limited too, so as to "see things from her perspective", in a way
— Regarding how I use names (first vs last), it's a mix of both. Depending on what their relationship to Y/n is, as well as if they’ve been “introduced to us” in this story yet. Such as, if a "new" character is brought in and she doesn't know their name, a description will be used for them until she hears from someone else what it is.
— Going off the previous point, I’ll use a character’s last name at at first, but later on if they become closer (friends) with Y/n, I’ll use their first instead. It also depends on whose POV it is (at least initially) in a section. So, for example, that means when we're with Katsuki, "Eijirou" is used instead of "Kirishima". But if we're with Y/n, it's "Kirishima". If either Katsuki or Y/n ends up appearing in the section after a POV has been established, the initial use of a name (either first or last) will still be maintained throughout until the POV is switched
'Text likes this conveys a character's thoughts'
— Because nobody quite knew the nature of her quirk, Y/n actually didn't know what it was until she was 12 — her first year of middle school. I highly doubt that's possible in-universe, but for the sake of my sanity, just pretend it makes sense;;

For info on reader's quirk, here's the document for it!

Chapter 1

Notes:

!! UPDATED APR. 2026 !!
What's New:
- Various changes/fixes
- New chapter name!

!! UPDATED AUG. 2026 !!
What's New:
- Various changes/fixes

AS ALWAYS:
Despite being proofread multiple times, I can't 100% promise there's no errors of any kind, so I apologize beforehand for any potential mistakes.

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

Chapter Text

CHAPTER ONE ; New Starts and an (Un)expected Encounter

Word Count: 2,943

 

It had been staring at her for a while now—the dreaded letter from U.A.

Though it merely lay at her desk across the room, minding its own business, Y/n could still feel its presence piercing through her, however hard she might try to avoid its existence. It was staying just within her periphery, a bright bothersome something sitting in the crest of her vision.

Whether it was an acceptance letter or a rejection letter was the source of the pit in her stomach. Right now, it was just a letter; the safe option. A regular letter's harmless. But the longer she let it stay there, hideously infecting her space with an aura of unease, the more she wanted to rip it open to get it over with.

“But that can wait for tomorrow” was what she wanted to tell herself for the umpteenth time.

Instead, finally, she got up from the edge of her bed to snatch it up, and stared at it in her hand.

Looking at it was a good start.

Despite thinking it was the worst timing to move back to the city now, in the throes of a war's backwash, Y/n couldn't refute her mom's unfortunately very sound reasoning of "we've been away long enough, and it's time you got into that school”.

Also because their allotted time for returning was quickly running out.

Since they had been living in the middle of nowhere, her knowledge on what had actually happened was limited; some big bad guys doing big bad things, and every capable hero pushing back against them—that was all she knew. But she did know that U.A was essentially the epicenter, and that she just might be waltzing right into a horrible mess of aftermaths.

The only time she ever saw anything remotely important broadcasted from the city was the last quarter of the infamous sports festival—which she was very surprised to see a certain someone participating in—and that was only because they had been visiting friends that were slightly closer to better reception than they were.

When they’d finally arrived back to the concrete jungle, how their newly constructed house had escaped virtually unscathed would be forever unknown to her. But she wasn’t any less thankful.

As soon as she could, she jumped on the chance to take the placement exam. As a result of everything that had happened, and all the restoration efforts taking place, it wasn't even remotely feasible to take U.A's regular exams.

What was offered, though, was a placement exam for transfers to not only automatically get you on the top of the waiting list for the practical exam, once doable again, but depending on how high your placement score was, you're even able to go to the school, and get put in a homeroom in the meantime.

Her eyes pored over the U.A. symbol embossed in the bright red wax seal on the envelope a while longer. Carefully, she lifted the flap, and the seal quickly renounced its hold to reveal folded papers inside. Her heart was in her throat while its beat drummed in her ears as she took the contents out.

At some point or another, Y/n had heard that students got a pre-recorded message in their letter, and she wished that, despite her not being an official student candidate, that she'd get one. But either the faculty had scrapped that idea for the new year, or she didn’t pass, because there was nothing other than paper in hers.

She hoped that it was the former, that it had become too much of a hassle for them to devise recordings anymore, and not because she had done embarrassingly poorly.

Cautiously, as if something hidden on the page was planning on leaping out at her, she opened the tri-folded paper. Immediately, she was met with a “Congratulations”, granting her a sigh of relief. With a lingering tingle of eagerness as her nerves could be at ease, she couldn’t contain her smile as she read on, giddy.

Whether offering a "trial" to new students was a way to discreetly measure one’s compatibility for the existing hero courses, or because they'd started to become desperate for new students after what just went down, she couldn't be sure. But the why didn't really matter to her all that much, because she got into her dream school.

Even though becoming a hero was something she’d grown up thinking about, practically shoehorning herself into that mindset, that was all it ever really was; the idea of it—being apart of a nationwide betterment, to be one of the good guys. Not so much focus on the details. Because if she actually thought about it for too long, she’d absolutely end up changing her mind.

And while part of her thought it silly to get back to working on her costume design before knowing if she'd even be accepted into the curriculum or not, she also knew there was no sense in selling herself short, either. She was capable and driven, so why wouldn’t she be able to pass the practical exam once the time came?

Y/n was beside herself with excitement, and the anxiety that she was riddled with had been diminished, sure, but there was still that one thing lurking in the back of her mind that was bothering her. He was at U.A. When she decided on trying to gain enrollment, she knew that was the case. But having that stop her from taking vital steps toward her dream career? Not a chance.

And so what if her quirk “isn’t suited for hero work”? As long as she used it the way she wanted to, that was all that mattered; as if he had any room to talk about what made someone a good person or not, let alone a hero. She couldn't let him win by holding that over her head for the rest of her days.

Yet here she was, still thinking about it. About him.

Hell, he probably didn't even remember her. What she should be concerning herself with was refining her costume's design, not about ghosts of bygones.

But the present does tend to fall victim to the past.

 


 

The days that followed the acceptance letter arrival came and went so quickly that it didn’t even feel real.

Even still, Y/n walked through the halls of U.A High School, alongside a boy that looked way too sleep-deprived, with the weight of misplaced uncertainty dragging at her heels.

The other boy in front of them began to come to a stop in front of a door—a door that she had to crane her neck up to see in its entirety—and turn to face the two behind him.

          “After I say what I must, I will announce your arrivals. Compris?”

Without any sort of confirmation, which she assumed was what he’d just asked for, the bandaged blond let himself in to the classroom, and slid the door closed behind him.

All the voices in the room were muffled, and if you really tried to you could make out the words, but Y/n was much too occupied with twisting the fabric of her skirt between her fingers.

Truly, she had no idea what to expect. Had no clue who was behind the door. This wasn’t her first time being “the new kid” at a school; having to figure out where she fit among the already-made cliques and hoping for the best—but this was different. This time it mattered. This time—

          “Transfer?”

The boy next to Y/n had spoken up, and all of her thoughts dissipated into nothing. She realized that he was ever so faintly putting out calming pheromones, mingling with a muted aroma of freshly brewed black tea. He must be a Beta.

She offered up a nervous smile with her sidelong glance.

          "Sorta, yeah," she breathes, giving her shoes one last once-over before looking forward. "I'm more of a tryout student, though."

          He hums passively in thought. "I've heard they're doing that for the start of this year," he says, "I suppose a war can throw off important plans, huh?"

She laughed lightly, feeling herself starting to relax. ‘He's harmless.’

          "Yeah, wars will do that to you." She’s fiddling with the skirt now, out of impatience. "But this might be the hardest part. First impressions and all."

Shouting, and bright blue lights strobing through the door nabbed her attention, but the boy seemed unbothered. And, actually..He looked familiar..

          “I wouldn’t worry too much. They don’t bite.” He pauses, reaching up to scratch at his neck. “Well, almost all of ‘em.”

          “How about you?” Y/n turns her head toward him with a tilt. “Is this your big debut, too?”

          “To the Hero Course, yes. Originally, I was in General Studies, but I finally managed to get transferred here afte—”

          An immediate click in her mind. “Ohh! You’re the mind control guy from the sports festival, right?” She’s feeling much more poised now, though it may be an attempt to override everything else in her mind; as an overcompensation. “I was rooting for you.”

          He smiles a lopsided grin at her. “Yeah? Why not the one with the flashy, powerful quirk?”

          “Flashy and powerful is fun and all, but..” She moves to idly hold one of her own wrists behind her back, shifting her weight in her feet. “Those guys have it easy.”

He raised a curious brow, intrigued, as if to tell her to go on, but then his regard snapped forward.

          “That’s our cue.”

Y/n wasn’t given the time to even take in a breath before he was sliding the door open. Instantly, excited shouts and rushing of bodies to the entrance was all she could perceive, and she ended up using the door as a shield between..whatever all that was.

          “Shinsou!”

          “You’re joining our class?!”

          “You managed to get the transfer!”

          “Sweet! You got your provisional license and everything?!”

There were so many voices, so many different scents, it wasn’t hard to get overstimulated—and she hadn’t even seen them yet. Right when she was about to step out from hiding, there was a distinct, pricking pain at her wrist that immediately had her pulling her arm back from behind her to look at it.

Her eyes magnetized to a spot just beneath her palm to see the kana 1 that were rapidly moving under her skin, like she’d just pulled the lever on a slot machine. Y/n felt like her chest just froze over. Of all the times to get her Call, she would’ve rathered she fell flat on her face as her first impression.

The syllabaries 2 went on and on, the entirety of the gojūon 3 running through itself several times over until it was slowing down. She found herself anticipating, waiting to see which one was going to stick, but the door was pushed further open to expose her.

          “Oh? Who’s that?”

          “Aoyama-kun said “new members”! That must be her!”

A deer in the headlights, she just stood there, dozens of eyes on her; at an utter loss for words. The tall, unkempt-looking man at the head of the room was her savior.

          “This is L/n F/n. She’ll be joining us as a trial student until we're able to get the practical exam sites up and running again.” He introduces, giving her an assuaging glance. 'He looks even more tired than Shinsou..’

This wasn’t the time to pay her wrist any mind. Fixing her posture, and taking a steeling breath, she lightly bowed to everyone in the room.

          She speaks more calmly than she feels, her mind racing miles a minute. “Thanks for having me!”

She feared if she were to show any sort of weakness, they’d be on her like a swarm of piranhas—she really hoped what Shinsou had said about them not biting was true.

But pleasantly surprised, they were just fine. Better than fine, in fact.

They were kind, they were politely curious, and they welcomed her, so clearly accepting of her that she felt silly for ever thinking otherwise. Immediately she felt like she was apart of something. If that wasn’t a good sign, she didn’t know what else would be.

The boy that had led them to the room—whose name she learned was Aoyama, and the source of that strobing light—started insisting on something about a farewell part. It made her realize that she really was being dropped into the middle of an entirely new world, a world that had already been well established and forged.

          "Mr. Aizawaaaaa, can we keep her?! Please?!"

          "Lower your voice, Ashido," the teacher, Aizawa, admonishes lightly, giving the pink girl a watered down glare.

Ashido, the girl latched on to her, was pushy, but she clearly meant well. Excited blooms of her fragrant, indistinct sweet scent whirled around them, trapping Y/n in a citrusy cyclone. She was probably an Alpha, like herself.

          "I wouldn't get too attached," Y/n laughs as she's being jostled softly, mostly teasing, but it's not a total lie either. "Who knows if I'll actually pass the practical."

Despite only knowing her for a couple of minutes, they're already overwhelmingly supportive, telling her to never take her dreams lightly, and that she'll become a full-fledged student in no time. Trying to ignore the pain at her wrist, though, was only second to her own eyes landing on a pair of familiar ones the more she skimmed the room.

          "Y/n? That Y/n?"

          "Izuku!"

Her eyes were darting all over Izuku's features as she managed to free herself from Ashido and take a few steps closer to him. His hair, his face, his stature even, they were all different than what she remembered. ..Especially the hair.

          "Man.. What happened to your freckles?" Her humorous, yet still concern-laden curiosity has both of them laughing, and Izuku’s shoulders rise with a decorous shrug, but he doesn't really have an answer. "And don't think I forgot to ask,” she preludes, “when the hell did you get a quirk?"

          "That's.. A long story, actually." He titters, rubbing at his nape at the query. "There's plenty we have to talk about, then."

They're chatting like they haven't been apart for several years, and it felt nice; familiar. And although they weren't really "besties" back then, right now, in a new environment, she'd happily cling onto the smallest bit of affinity. Y/n briefly caught a faint whiff of a sagey something, and she remembered that she never got to find out what he presented as before she left. They share the same designation, if she had to guess.

The other students just watched in silent awe, looking back and forth between them like they were a thought-to-be extinct species of animal interacting.

          Izuku's eyes suddenly light up. "Oh, right!” He lightly moves aside, faintly gesturing with a turn of his head to the other side of the room a few desks away. “You wouldn't forget Kacchan, right?"

She saw that unmistakable blond hair, and her whole body became rigid before she put on a smile and nodded, saying some dumb lie about how it felt like only yesterday they were in grade school competing to get their drawings pinned up on the corkboard, displayed to the rest of the art class for that week.

As much as she didn’t wish to acknowledge him, it was unavoidable if they were going to be classmates, whether she liked it or not. He was just as bandaged up as others were, vacantly staring down his desk while everyone else was still crowding the door, who were now back to interrogating Shinsou like ravenous reporters. She was curious as to how he got so banged up, but asking about it wasn’t something she saw herself doing any time soon.

After he'd heard his name a little ways away, Katsuki indolently swiveled his neck, completely uninterested. But his focus hardened when their eyes met. He sat up in his seat, a look of disquiet cast onto his face.

Thanks to the all the medication he was put on, the past few days have been hazy and mostly a blur. On a normal day, he barely registered the happenings in this classroom anymore, practically numb to it by now, but as of late it was twice as bad.

This was way too specific of a situation to be a drug-induced delusion, however.

          "You've seen better days, I take it?" Says Y/n.

She was trying her absolute best to stay composed, to be as unbothered as she could appear—despite those words being the first ones she’d spoken to him in half a decade. The hurting of her wrist made her face twitch, feeling as though a scorching wire was slithering through her veins, and a hot iron branding her skin at the same time. She might've been able to convince herself that she smelled burning flesh. But she endured it. She had to.

Katsuki didn't know what to say.

And the deep, aching sting in his chest wasn't helping. Weren't the meds supposed to get rid of pain?

"Why are you here?" was at the tip of his tongue, readying itself. But to no avail.

While he just sat there, staring like an idiot trying to open his mouth that suddenly felt too heavy to, Izuku was ushering her to an empty desk, which was the one behind his own.

Nothing could have prepared him for something like this. Though he knew that that wasn't completely true—all she ever did back then was rave about becoming a hero; of course she would've made her way here at some point or another.

..Of course?

Notes:

remember, be sure to read the document linked in the beginning notes for details on how y/n's quirk works!!!

˚₊‧꒰ა FOOTNOTES─.✦

1 the system of syllabic writing used for Japanese, having two forms, hiragana (ひらがな) and katakana (カタカナ) [ Return to fic ]

2 a set of written characters representing syllables and (in some languages or stages of writing) serving the purpose of an alphabet [ Return to fic ]

3 In the Japanese language, the gojūon (meaning 'fifty sounds') is a traditional system ordering kana characters by their component phenomes, comprised of a 5×10 grid of said kana that corresponds to one sound in Japanese [ Return to fic ]
˚₊‧꒰ა END NOTES─.✦
i'm sorry that y/n's transfer literally makes no sense sdfjhsdjhkf tried my best to make it work okay 😭 it's fine, everything's fine
*copium*
just wanna to throw out there that this is my first stab at writing a chaptered story, so if that’s prevalent, i apologize :’).. i’m so used to doing oneshots, my brain is seriously struggling to grasp how to properly do it.
i already have the next few chapters written >:3c (as of right now, the current completed chapters (including this one) have a total of 14k words!!) thank you to those that helped me beta this trainwreck !!
✎𓂃 fun fact:
the entire premise of this fic stemmed from my desire to live vicariously through a character that could pretty much keep katsuki in his place because he pissed me off so much (i’d gotten the idea well before his development/character arcs) LMAOO.
..although the a/b/o thing was kinda impromptu and i hesitated on whether i wanted to implement it or not (because this is also my first attempt at writing soulmate stuff), but i bit the bullet and did it anyways. the concept of “reassignment” probably isn’t 100% original, but eehh.. it was originally for a bkdk a/b/o fic i had first drafted at least 7yrs ago (holy fuck that was so long ago) but i thought it’d be interesting for this one instead!