Archive of Our Own ^beta

Chapter Text

Midoriya Izuku was out of luck. Being a late bloomer at 12 years old, one of the most delayed cases of all time, would do that to you. Everyone called him the “quirked quirkless”, Deku, useless, and any other sort of atrocities. It was normal, his day to day life. He hoped for a quirk that should theoretically come any moment, but seemed oh-so far away.

This day was particularly bad, being that Kacchan had found his Analysis For The Future 9 notebook, and had not been pleased after reading his “stalker notes”. Cue to the much harsher beating today compared to other times, just after the end of school. He was knocked out for a long time, and then just layed there still to try and quelch the pain for a while more. It had likely been over an hour since the end of classes, and there was no one in the building, apart from some of the cleaning staff, and maybe some professor doing paperwork.

Then, he felt something inside himself. He felt his body twisting and changing in impossible ways. His injuries made their refusals known, and were promptly ignored by the force playing with his body like it was Play-Doh. He felt his skin grow heavier, his limbs shorter, his innards rearrenging. And then he saw it, dancing over his eyes.

<Welcome, User Midoriya Izuku. Your quirk has finished developing and User has been declared to have enough mental maturity. Quirk manifestation is in progress. User will be temporarily incapacitated>

Before the world faded to black, he saw as his skin turned to crystal, and felt as his face receded into his body much like his limbs were doing. As this was happening, one thought ran through his head.

What the hell is happening?!

And then he passed out.

*********

Detective Tsukauchi needed more coffee. He also needed answers, but coffee was the priority.

Everything started like every work-related headache starts: with a very frantic call, some troops sent to investigate, no one getting clear answers, and then throwing him into the mix as if he was a secret weapon that, from so much use, was losing the “secret” part. Then, the final ingredient for True Chaos™ was him also not knowing what the hell was happening.

Two hours ago some staff from a local middle school named Aldera Junior High called after they were somehow warped out of the facility, and a forcefield appeared around the whole place keeping everyone out.

The theories right now went from a quirk incident to a villain taking the place hostage for some reason.

He was right now right beside the dome, staring at it as if glaring hard enough would give him all the answers one could hope to get. No answer came.

He sighed, walking towards his patrol car to grab his backup coffee for situations like this, watching as the police and some lesser known heroes kept the press out, which were loudly asking questions for which no one had answers.

He wanted peace, coffee and answers. The first he had given up on the moment he joined the police force, the latter was still a work in progress, and the second was running out.

*********

Izuku awoke with the strange feeling of not feeling. He could not feel his arms, nor his legs, nor his face, nor his heart. He tried to look around, which he could, as he observed the classroom around him with what could only be called familiarity, but not the one you would call something you have had a lot of interactions with, more so how you would call a part of yourself. The classroom felt like him , which was all sorts of weird.

Then he saw it, resting where he once had, a crystal sphere that felt more like him than anything else. All other things were like hair: you, but not really. This was as close as looking to one’s own heart as one could, or at least that’s how he felt.

What is going on!? Why am I floating, why am I the classroom, and why am I a crystal ball!?

Then, something appeared in his vision.

<Hello, User. Installation of quirk has been successful, and as such you have been awoken.

I am your guide and who will explain to you the inner workings of your quirk>

Izuku took a moment to read and re-read the message. He… He had a quirk! a godforsaken weird, but he had one! But… What does it even do?

<Your quirk, User, is called Dungeon Core. Your quirk turns you into a crystal ball who has a god-like power over their domain. You can create beings to populate and defend you, and are advised to form a symbiotic relationship with the local populace to grow stronger>

That gave him lots to think about, as he realised his life had just been flipped upside down. His mother… What about his mother? Would he never be able to talk to her again?

<Contact with the outside world is possible, but complicated. It is recommended that the User delay this thought process for another time>

Okay, okay… It’s just a “see you later”, not a “goodbye”. Can… Can you go over my capabilities in greater detail to know what to do?

<Request accepted.

Right now, you have domain over what used to be the Aldera Junior High school grounds, and as such, you can change the environment and create beings to populate the place.

You have different affinities with different concepts, elements, objects and materials. When you want to create something, the higher your affinity with what you use to create it and what you are creating, the easier to make and the less it will cost to make its spawn point. There is a limit of spawn points and strength of inhabitants per floor.

Inhabitants can be created and shaped by your thoughts if you will them to, and don’t have many limits on what can be done, as long as it is within the limits of your affinities. Do bear in mind that Inhabitants will cost less to make and take less spawn point space if they match with the theme of the biome, in this case [Aldera Junior High - Middle School]

Spawn points are from where your inhabitants appear after being designed. Every time one dies, it will reappear in its spawn point after some time. To make a spawn point you need to have already designed its destined inhabitant, and it will also cost mana, fluctuating with how powerful it is.

Mana is generated naturally by you, but your main source will be from [Adventurers] who either defeat or are defeated by inhabitants. Mana will also be consumed when giving them rewards for clearing a floor or opening a chest put there at your discretion. You can either create custom-made rewards, or let a RNG program run it for you, with customisable options.

When an outsider enters the dungeon they choose how they want to present themselves. If they choose to present as [Adventurers], that means inhabitants will act according to their natural aggression patterns and rewards will be given accordingly. However, they will be unable to damage the User, and the User will gain mana from their inhabitants either defeating or being defeated. When [Adventurers] are defeated through lethal means, they will reappear uninjured outside your domain. When an [Adventurer] receives damage that could either be permanent or serious, like dismembering or broken bones respectively, they will recover once outside.

If an outsider decides to present themselves as an [Intruder], they will gain the ability to damage the User, and the User will not gain mana from their inhabitants being defeated by them. However, the [Intruder] will not receive any reward from clearing floors or going through chests, all inhabitants will aggro them when in the same floor and safe to do so, and once defeated, the fate of either death or unconsciousness for them is yours to decide.

You can also designate Floor and Biome bosses, which lets you create and spawn a monster with a higher mana cost and strength than normally allowed, and which have to be defeated to go to the next floor.

You will gain affinity with any object being carried by defeated outsiders, with things relating to defeated outsiders (like quirks, mentality, personality, etc), and with things already within your domain when you expanded, excluding sapient beings.

There is also a number of unlockable blueprints that will be given to you by the same guidelines as said above, and when making something close to it when making an inhabitant>

Well, that was definitely in detail. Let's see… Create inhabitants, gain mana, attract [Adventurers], discourage [Intruders], expand affinities. Well, that just irradiates ‘simple’, does it not?

Chapter Text

Izuku’s mind was running at 100 miles per minute, racing with thoughts about what this would mean for him in the long run. When would he see his mom again? How would he go to high school? How would he compensate for what essentially is property theft? He was thinking of every little thing that could go wrong for him. And in true Midoriya Izuku fashion, he did the one thing he did when a problem he could not control was presented to him.

He ignored it until it went away. Or it bit him in the ass later. We’ll see what happens first.

Instead, he chose to try and take a look at himself. Not the classroom, and not his core, but what he was actually seeing through. He figured out pretty quickly that his spectral self was not visible, and not corporeal. It was a disembodied consciousness that allowed him to navigate through his domain unperturbed. Domain which expanded beyond the classroom, and through the whole school, finishing just beyond the entrance, and he could not look beyond.

Hi core was in the first floor, in which there was also the gym, more classrooms and some closets.

Just as he remembered it.

Before his thoughts could wander to his more preoccupying concerns, he decided to go shoulder deep in making inhabitants to both defend and distract himself.

Let's see…  I have to make an aggressive being that fits in a school and can defend me. Well, isn’t this an easy decision?

Bullies. He was going to make bullies.

To start, he was going to experiment a little. He grabbed not flesh and bones to make its body, but negative feelings. Hate, Defamation, Cockyness, Arrogance. He saw as the negative feelings took on a humanoid form, devoid of features, made of a purplish-black substance that looked liquid, but was solid. He had a decent affinity to this feelings due to being the target for them daily.

<New blueprint unlocked: [Tenebris reliquiae (Dark Remain)]

[Tenebris reliquiae (Dark Remain)]

A being made of negative feelings and concepts, meant to represent something that shouldn’t have been. Highly customisable>

Well, that was a blueprint, apparently.

Next, he gave the bully a male uniform, and a face. Not much of a face, more like red eyes that glared hatefully at everything and a cruel smirk that comforted no one. He also gave it some hair.

After a moment he decided to test something.

Can I save this as a blueprint?

<Custom blueprint saved: [Tenebris reliquiae (Aldera Junior High male bully) lv 3]>

Yeah, that works. Then, he made a female bully, more or less the same, with hair just past the shoulders, female uniform and appropriate proportions (If he got embarrassed while making it, that’s between himself and his quirk).

<Custom blueprint saved: [Tenebris reliquiae (Aldera Junior High female bully) lv 3]>

Okay, I now have my main defenders. Now, what quirks do I give them? And then he started looking through his affinities to see what would make for a decent quirk to give to his new inhabitants. Some options presented themselves, seemingly because of different reasons.

He had a very good affinity with telekinesis due to both his familial relation with his mother, and his personal one with her too. With fire, it was also very good because of his father’s quirk and because he was the victim of a fire-based and fire-like quirk daily. This is also why he had a decent affinity with explosions, but he decided to stay away from that one for now.

That would work for now. He willed the concept of fire to take the idea of a basic fire quirk and gave it to the male one, doing the same for the telekinesis concept and giving it to the girl. Before saving the blueprints, he tried to abbreviate the names.

<Custom blueprint saved: [Tenebris reliquiae (AJH M. bully: Basic fire quirk) lv 8]>

<Custom blueprint saved: [Tenebris reliquiae (AJH F. bully: Basic telekinesis quirk) lv 8]>

Seeing his success, he decided to summon them in the neighbouring classroom to his core. 

<Spawn points placed.

Mana: 84

Spawn points: 1.6/10>

As soon as they appeared, they stared at each other for a moment.

“What are you looking at, udder bitch?” said the boy.

“The face of an idiot” said the girl.

Wait, they can talk? How…

<Due to putting high amounts of Defamation in them, they can talk for the purpose of insulting and defaming others>

That makes sense, I guess… As long as they don’t try anything, it should be good. Before anything else, another thought came to him. Wait… Can I move my core to another place?

<It’s possible to move your core in exchange for 20 mana>

Then, please move it to the rooftop.

<Moving commenced>

Izuku saw as his core was covered in light and disappeared. Then, he felt it reappear at the top of the building.

Okay… Now let’s see about making that boss.

He took the basic [Tenebris reliquiae (AJH M. bully)] blueprint, made it older, bigger than normal, gave it P.E. clothes, and used the concept of A Beating to make his quirk, which increased his strength and made it partially bypass the target’s durability.

<Custom blueprint saved: [Tenebris reliquiae (AJH M. P.E. teacher: Beating quirk) lv 15]>

Then, he made it a boss.

<Floor Boss designated: [Tenebris reliquiae (AJH M. P.E. teacher: Beating quirk) lv 15]. 

Floor lv limit: 10. Floor Boss lv limit: 15. 

Request Accepted. Please place spawn point>

He placed it in the middle of the Gym.

<Spawn point placed.

Powering up Floor Boss>

Then, Izuku watched on as the inhabitant grew even bigger and stronger than it already was.

<[Tenebris reliquiae (AJH M. P.E. teacher: Beating quirk) lv 15] has successfully been summoned as the Floor boss.

Mana: 68

Spawn points: 2.8/10>

The teacher made of solidified liquid hate looked around the gym, huffed, and sat down.

After that, he started summoning more bullies to populate the rest of the school. First, he moved the first 2 bullies’ spawn points from the classroom to the opposite hallway (Thankfully not too expensive, just 2 mana each), created another pair in the other hallway, another in the entrance, and 2 more in the gym, and with enough space for one sole bully that he was going to put in the gym with the other 2 pairs, he had to wait for his mana to regenerate.

Natural regeneration was, admittedly, very slow. 1 mana each half hour. Which meant a 3 and a half hour wait (He had already gained 1 during his inhabitant placing).

Then, everything shook.

*********

Tsukauchi was not a fan of brute forcing things. He liked to be methodical, drink coffee while thinking things through and asking the right questions.

But there was no coffee left, and no one to ask questions to. There had been no contact, no trace of the missing middle schooler (He still remembered the flimsy hope he got when he heard of a woman asking for her missing son who attended this same school, a possible lead, but which had just led them straight back to ‘We don’t know what is happening’), and no ramson attempt. It was as if the place had been closed for remodelations.

That led to All Might being called in, and asked to break the barrier. He watches as All Might goes in front of the giant dome, and everyone finds cover.

“TEXAS… SMASH!!”

He smashes his punch into the giant dome, the air pressure sending shockwaves all around.

As Tsukauchi looks up from around the patrol car, he spots a wide, 1 meter radius crack around All Might’s punch’s landing place, which quickly begins to regenerate.

“HM, IT LOOKS LIKE IT’S STURDIER THAN I THOUGHT. THAT JUST MEANS I’LL HAVE TO PUNCH HARDER! TEXAS…!!”

<Please, stop. You are scaring the User>

That made All Might stop, which made everyone look up curiously at the reason for his abrupt interruption. Tsukauchi gaped.

“F-Finally… Contact!” He yelled, as he run up to the giant blue screen floating in front of the massive hero “Who… who are you!? What are you doing with the school, and who is ‘User’!?”

The screen flicker out, and a new one appeared.

<I cannot disclose that information> True

His face scrunched up in irritation and confusion. “Has the boy inside there been harmed in any way?” He asked, calmer than before.

<No> True 

He sighed in relief. “Then what do you want, villain?”

<I’m not a villain> True 

“So this is not a villain attack?”

<No> True 

“Then what is happening?”

<I cannot disclose that information> True 

“Why is there a forcefield around the whole school?”

<I cannot disclose that information> True 

“When will we be able to enter?”

<Approximately 3h, 30m> True 

“What is happening inside there?”

<I cannot disclose that information> True 

Tsukauchi sighed “This is going to take a while”

He already felt the need for more coffee.

*********

Izuku stared at the regenerating crack in his domain with dread as the system informed him of the problem.

Apparently, the authorities didn’t like a forcefield surrounding a whole middle school. Who would’ve guessed! Now, he has to sit here, scared, and wait ‘til he places his last inhabitant to be able to open his doors.

Fun.

Chapter Text

Tsukauchi looked at his phone again. It was 8:15pm, 30 minutes before they would be able to enter. They still didn’t know anything about what was happening inside, and the blue messages had stopped responding to him. All Might hadn’t stuck around long after that, being that his time limit was still a thing.

Eraser should be starting his patrol right about now, maybe I should call him to have more backup. Except two, the rest of the heroes have left this area after nothing happened, and the ones here are support heroes, better at dealing with hungry paparazzi and post-attack rescue and management.

With his mind made up, he contacted Eraser through his earpiece.

“Eraserhead, this is Detective Tsukauchi speaking”

“ Hear you loud and clear, detective ” A tired voice answered back.

“Your help is required at XXX, between XXX and XXX, at a location known as Aldera Junior High, in 30 minutes”

“ Understood. Does this have anything to do with that forcefield thing I heard about? ”

“Yes, I’ll be giving you a rundown when you arrive”

“ Copied ”

And then he heard the connection be cut off.

Then, he cursed. He forgot to tell him to bring coffee.

*********

Shota didn’t know what to expect when he arrived, 5 minutes earlier than requested. Well, that’s a lie. He did know one thing to expect: a very tired and coffee-craving Tsukauchi.

He threw a jelly pouch at him, which he took and sourly drank. Not as good as coffee, but it will suffice for now.

As he waited for him to finish, he started up the conversation while curiously looking at the dome surrounding the school.

“So what do we have here, detective?”

Tsukauchi sighed as he finished the jelly pouch, “Not a lot is known, just that this supposedly is not a villain attack, and that  there is a boy inside that is supposedly not been harmed. Also, there is an entity that speaks through blue, floating messages, and that when All Might tried to break through, it said that he was ‘scaring the User’”

“Who’s the boy?”

Tsukauchi handed him a file “Izuku Midoriya. A 12 year old boy student at this school.”

As he scanned through the file, he noticed something interesting, “Quirk: NYM. That means ‘Not Yet Manifested’ if I remember right. You think that could be the cause for this?”

The detective nodded, “Is the leading theory, yeah, but nothing is confirmed until we can enter through that forcefield”

Then, as if answering to his prayers, the dome shone slightly, before dimming to its usual light blue color, but now with the outline of a square the same color across the floor.

Everyone stilled.

Slowly and carefully, officer Tamagawa slowly stepped towards and into the square. Then, his feline eyes widened.

“Detective, you have to see this!”

Taking his words for what they were, Tsukauchi approached, Shota not being far behind. Both stepped into the square.

<3/4 maximum players:

Tamagawa Sansa

Tsukauchi Naomasa

Aizawa Shota

———

If you are ready to continue, please state so>

Seeing this, and deciding to be better safe than sorry, he called on one of the closest officers.

“Officer Tokunaga, please step in the square”

The officer complied, stepping in the square. After her name appeared in the message, everyone voiced their readiness.

<3/4 maximum players:

Tamagawa Sansa READY

Tsukauchi Naomasa READY

Aizawa Shota READY

Tokunaga Shika READY

Before connecting to server, please state your intent:

[Adventurer]: You do not seek harm to the User and its dungeon, and only rewards. If you were to be defeated, no matter how lethal the means, you will reappear outside the dungeon unharmed. You are not able to harm the User in any way.

[Intruder]: You seek harm to the dungeon. Rewards will be cut, inhabitant aggression increased. You will be able to harm the User>

Tentatively, everyone chose [Adventurer].

Then, everything faded in light blue light.

<Connecting to server…>

*********

The sensation Izuku felt right now was very trippy. He felt like there were two simultaneous dungeons at the same place and time, but also not.

What is happening?

<When a party enters your dungeon, a new server is created through quantum superposition. Both things are real and both things are happening. You can see the active server numbers here:

Server 0

Server 1

Any change to the dungeon has to be made through server 0, and it will affect every server activated after the change. Your maximum server quantity is 10, counting server 0>

Ha, interesting. So everyone who enters will always have a dungeon full of inhabitants.

<That’s correct>

As he saw the party appear in a flash of light blue in the border of his domain, he saw someone… familiar. He recognised him from somewhere. He analysed him closer. Long, grey scarf, yellow goggles, black long hair and jumpsuit.

Is that… Eraserhead!?

If he could, he would’ve passed out.

*********

Shota looked at the school entrance before him. With a shared nod with the three policemen with him, he opened it. The first thing he saw was an average school hallway with a staircase going up right behind a pair of… something.

They looked like Middle schoolers wearing the normal Aldera Junior High uniform, but something was wrong. They had glowing red eyes, a smirk that looked unnatural, and their skin, if it could even be called that, was made of a liquid looking black-purplish substance. But above all, they emitted a sense of wrongness and hate that made him get on edge.

The duo looked in their direction, and their smirks widened.

“Well, well, look what we have here, a hobo and his three street dogs behind him”

“Really, my friend, how can you stand being so useless that you don’t even know how to take a shower?”

Shota ignored their comments, and after looking at them closely, he realised something.

“They’re quirk constructs!” And just as he said that and got into a fighting stance, the boy’s hands lit ablaze, and the girl’s right hand shone light green as he felt a force collide with him and attempt to push him back.

He activated his quirk, and both effects stopped, just as they were shot down by the police officers. They both dissipated in purplish-black smoke, which condensed into… a pen and pencil, and 150 yen.

The four shared a look with each other and got closer. As they got closer, they noticed that the hallway branches into two separate ones. And that the staircase has a forcefield like the one outside.

<Defeat Floor Boss to proceed to next floor>

“I believe it would be better to separate. I and Tokunaga will go this way,” He pointed to the left, “And you two go the other way.”

Tsukauchi nodded,”I believe that would be for the best, yeah”

As they separated, he went through the hallway looking into the classrooms he passed by. The first one didn’t have anything, and before he could check the second, he spotted a duo of students around the corner.

Silently, he signaled to the officer to stop and devised a plan. They were too far and the hallway too unobstructed to get in range, so he’d disable their quirks and she would shoot them down.

He stepped into the hallway, disabled their quirks, and heard her shoot.

*BANG* *BANG* *BANG*

He watched them fall to the ground, and condense into a ruler and a marker.

He shared a nod with the officer, and they went to check the second classroom. There was a discarded male school uniform on the ground, a backpack, and a burnt notebook to the side.

As he got closer, his thoughts raised, Unless this was discarded before the dome creation, this is likely from the missing kid. Which would mean he has a quirk that makes clothes not necessary or useful.

He started examining the burnt notebook as Officer Tokunaga checked the backpack.

He– —-sis for –e fut— 9

As he went from page to page, he eventually found something that surprised him.

Eras—head

—-rk: Erasure

Des——on: Allows the user to ————— erase — quirks of oth— as long — he — star—…

From there it devolved into what looked like a detailed description of his quirk, fighting style, support gear, etc, but he couldn’t read it due to its bad state, and the awful handwriting.

As he went back to the first page, he saw the kid’s name written in the same, barely distinguishable handwriting.

Iz–ku Mid––ya

“Looks like this is from the kid,” he said, drawing the officer’s attention, “this is signed by him.” he lifted the book.

“This stuff looks like regular highschool student stuff,” She said as she continued looking through the backpack, “nothing out of the ordinary.”

After a while, they continued their way into the hallway. Before they could do anything, they heard gunshots coming from inside one the big double doors, along with panicked screaming.

SHIT!!

And then he rushed to the door, officer Tokunaga close behind.