Nearly twelve hours had passed since Izuku had been kidnapped. The fog villain, Kurogiri, would pop in every now and then to check up on him, but for the most part he was left alone. Kurogiri hadn't even bothered to confiscate Izuku's phone. He'd immediately tried calling for help the first time he was left alone, of course. It wasn't all that surprising to discover that his phone had no reception, although there was a closed Wifi network he didn't have the password for.

Even top-secret supervillain hideouts had to have Wifi access in the current year.

Kurogiri didn't bother to stop Izuku from actually leaving the room either, which was confusing. Was the villain really that sure he wouldn't be able to escape? He decided to walk around and explore for a while, mainly to help to keep his thoughts off what he'd learnt the day before.

Izuku still had no idea how he should feel about an almost mythical villain claiming that he was his father.

The Registry of Japanese Supervillains was a dark mirror to the more famous Hero Billboard Chart, both of which were published by the Hero Public Safety Commission. All For One was right at the top of the HPSC's list, the only SSS-ranked villain operating in Japan. Although there was no name, photo or description of him, just a question mark and a title: the 'Rumored leader of the Japanese underworld'.

Izuku normally wouldn't have thought twice about a villain, especially one that might not even exist. But according to his Mom, it was because of this villain that his father had died. Izuku didn't feel like getting revenge or anything, yet he was still curious. He'd ended up spiraling down a rabbit hole of sketchy rumors and questionable online forums to find out more about this mysterious cryptid.

From what he could find, Japan's top supervillain was only ever referred to obliquely or by a series of pseudonyms. He was mostly famously known as 'Enma', a reference to an old deity who was the ruler of hell and the penultimate judge of the dead. Enma's status as the so-called 'Demon Lord' and the legendary 'Shadow Emperor' of Japan seemed to go unquestioned even by the most hardened criminals.

There were two particular rumors which stuck in Izuku's mind. The No.1 villain had apparently been around for centuries, and he could somehow steal Quirks! Anyone else would probably find this absolutely horrifying, but for Izuku – well, he was pretty much resigned to being Quirkless anyway, no matter what anyone else said. He could definitely see how such a power would cause the government to give the villain a triple-S ranking.

In comparison, even the infamous 'Grand Commander of the Meta-Liberation Army', Re-Destro, was only SS-rank. Re-Destro, who had personally led eight different insurrections against the Japanese government, whose Meta-Liberation Army was a declared terrorist organization, who had once managed to fight All Might himself to a standstill!

Izuku's stomach suddenly decided to announce its displeasure with a growl, abruptly reminding him that his last meal had been lunch at school yesterday. He realized that he was completely lost. The dark hallways and empty rooms of this building all looked the same to him.

It was in an enormous, deserted arrival hall that Izuku finally gave up trying to make his way back by himself. "Um, K – Kurogiri?" he called hesitantly. He stumbled backwards in surprise when a dark portal opened right in front of him.

Kurogiri stepped through and bowed politely to him. "How may I be of service, Izuku-kun?"

With the way he spoke and his formal attire, the mist-man could easily pass for a stereotypical Western butler. "I – could you take me back to the lounge? Please?" he asked uncertainly.

"Certainly." Another portal opened immediately and Izuku only hesitated for a moment before following Kurogiri through. "Was there anything else you needed?"

Izuku took a moment to recover from the jarring transition. "Could – could you get me something to eat? I haven't eaten since yesterday."

"Of course. Please have a seat, I shall return shortly."

It was just after one in the afternoon, according to Izuku's phone. Kurogiri warped in with a small stack of delicious-smelling takeout containers several minutes later. Izuku was hungry enough not to question if the food was poisoned or something and simply devoured everything.

Although it was creepy, having Kurogiri watch him while he ate. The evil butler didn't even do anything, apparently satisfied to just stand there and stare at Izuku in complete silence. The containers disappeared into another portal once Izuku was finished, leaving him sitting awkwardly in his chair. What the heck was he supposed to do in a situation like this?

"Th – thank you," Izuku said finally. It felt strange, having to thank the villain who was responsible for kidnapping him.

"I am here to serve, Izuku-kun," Kurogiri bowed yet again. "Please do not hesitate to ask me for anything you require."

Another awkward silence descended upon the room. Well, it was awkward for Izuku, but Kurogiri didn't seem to care. He simply stood with his hands neatly folded behind his back, patiently awaiting the next instruction.

In the end, the silence was broken by Kurogiri himself. "It appears that I have been called away once more," he said suddenly, despite Izuku having heard nothing. "I shall speak with you later." The mist-man stepped through another warp gate, leaving Izuku blissfully alone once again.

Yet it was barely a minute later when black fog billowed out into the room once again. It cleared to reveal Kurogiri as expected, except that he wasn't alone this time. The butler villain was accompanied by another teenage boy. He had blue-grey hair and horrible bags under his eyes, as though he hadn't slept for a week.

"So this is the kid, huh?" said the teenager. His eyes narrowed as he looked Izuku up and down. "This is Sensei's long-lost child? He's kinda plain looking, isn't he? I thought he'd be eight feet tall with like a dozen different Quirks or something."

Given that description, there was only one person whom this 'Sensei' could be.

"Be polite, Tomura-kun," Kurogiri chided. "You are correct, this is indeed your Sensei's son. His name is Midoriya Izuku. I would appreciate if the two of you could try to get along."

The teenager, Tomura, simply shrugged. "Fine, whatever. Hey kid, you play any video games?" he said, in what could almost pass for a friendly tone.

"Not – not really?" stammered Izuku, completely taken aback by the older boy's cavalier attitude. He absolutely did not expect to be asked about video games after being kidnapped and held in a villain's lair.

Tomura rolled his eyes, oblivious to Izuku's internal thoughts. "Great. Sensei's son is a giant fucking normie. How can you not play any games at all? Little kids like you obviously wouldn't have anything like a proper gaming rig, but don't you guys have phones?"

"Yes, but, um, I don't really play any games," said Izuku uncertainly.

"Is this an out-of-season April Fool's joke?" Tomura asked incredulously. "What kind of – you know what, let me just show you all the crap I've got on my own phone. There must be something you'd be interested in."

An increasingly bewildered Izuku could only watch as the other boy proceeded to run through what looked like dozens of games on his phone over the next few minutes. He eventually settling on one which had cute caricatures of pro heroes battling each other. Watching a chibi All Might suplex a chibi Endeavor wasn't too bad.

Izuku had no idea what happened, but the situation quickly deteriorated. Apparently, Tomura had lost because his opponent cheated? What followed was an uncomfortable, ten-minute-long rant which left Izuku cringing internally with second-hand embarrassment. Even Kurogiri was unable to reign in the teenager, who started throwing a tantrum like a spoilt child.

"Tomura-kun, I would hope that you –"

"Fuck off you malding mist man!" Tomura screeched. A wave of disintegration spread out from his fingertips, dissolving his phone into ash and travelling down the furniture to eat away at the floor. He jumped up and started spitefully swiping his hands across whatever he could reach.

Luckily for Izuku, Kurogiri quickly evacuated him to another part of the room before he was in any danger. In the end, Tomura was only pulled out of his tantrum when another portal appeared. The room was once again flooded with that oppressive, controlled aura which heralded the arrival of All For One.

The sheer amount of damage done didn't seem to faze the disfigured villain at all. In fact, All For One seemed to be in a positively good mood. "Good afternoon Tomura, Izuku," he greeted them smoothly. "I hope the two of you are getting along well."

Izuku opened his mouth to say that no, they weren't really getting along, but received an elbow to the side before he could say a word. "Of course we are, Sensei!" said Tomura, putting on a horribly cheerful voice. "Izuku and I are best friends now, right?" The sheer amount of reverence almost radiating from the teenager was quite disturbing.

"Excellent," said All For One, bringing his hands together. He either did not notice or more likely did not care at all about the destruction Tomura had caused. "Now then, I do think it is time we continued our conversation from yesterday, Izuku. Tomura, you may go and... well, go and do whatever it is that you normally do when your presence is not required."

The blue-haired teen didn't seem to hear him, stuck in a state of worshipful admiration.

All For One sighed. "I would like to speak to my son alone, Tomura," he said loudly. "Go away."

"Of course, Sensei," Tomura finally managed to say. He bowed nearly ninety degrees at the waist before vanishing into another portal with Kurogiri.

Izuku sank into an intact chair with a grimace. Even Tomura's lousy attempts at being friendly were better than being alone with All For One. The disfigured man sat himself down across from Izuku, not bothered at all by how Izuku petulantly refused to look at him.

"So, have you had time to absorb what we discussed yesterday?"

"I don't care what you said, you're not my father!" Izuku immediately snapped. "My dad's not a villain, so you can't be him."

"Why, I'm almost disappointed," All For One said mockingly. "I thought you were more open-minded than that, Izuku." He leaned forward conspiratorially. "I'll let you in on a little secret: that divide between 'heroes' and 'villains'? Well, it's a distinction which doesn't actually exist! There are no sides, no rules, no good or evil in this world. There is only power, and what you choose to do with it."

"Of course you'd say something like that, you're a supervillain!" Izuku scoffed.

"Does that make my statement any less true?" All For One asked. "Even amongst your vaunted heroes it is always the strongest who rise to the top. The greatest champions of justice and the most heinous of evildoers are both defined by their power, by their ability to enforce their will upon others. It is entirely normal for those without power to be completely ignored."

A small spark of defiance burned brighter in Izuku's chest. "You're wrong," he insisted stubbornly. "It doesn't matter how strong or weak you are, a hero is someone who helps other people! That's what All Might says!"

"How convenient then, that All Might is also extraordinarily powerful," said All For One dryly. "I'd argue that he is in fact the textbook definition of 'might makes right'. How far do you think his integrity would go if not for his tremendous strength? How many of his principles has he enforced at the ends of his fists?"

Izuku scowled and clenched his jaw, not knowing quite what to say.

"Strength is all that matters, my son. You'll find that out for yourself, eventually." All For One folded his hands together, silently studying Izuku once again with that sightless gaze. Yet Izuku refused to be cowed, glaring defiantly at the disfigured supervillain.

"I was not an only child, you know," All For One finally continued. "My dear little brother – your uncle – was much as you are now. Morally principled, a strong belief in justice, integrity and all that other nonsense. We would clash often over his ideology, yet Yoichi was simply too weak to have any hope of opposing me."

"Wh – what happened to him?" asked Izuku. He was shocked to see All For One's mutilated features twist into something approaching regret.

"My brother continued to defy me, despite my best efforts to reconcile with him. Sad to say, the two of us eventually came to blows. He was no match for my power of course, yet his detestable ideals kept him fighting me right to the very end."

All For One laughed, bitter and cold. "My dear little brother, led astray by foolish dreams of righteousness and morality," he sneered. "Kindness, ethics, justice – all of it meaningless drivel which only served to drive him to his death at my hands. Outdated beliefs which only serve to shackle the strong, to the weak."

A heavy silence settled on the room. All For One appeared to be lost in thought, while Izuku had no idea what to say. No, there was one thing he wanted to ask, but he was almost afraid of the answer. Yet the silence stretched on, until Izuku was finally able to overcame his reluctance to speak.

"If strength is all that matters, then why'd you kidnap me?" he eventually managed to ask. "I'm just a kid, I'm not strong or powerful at all. I - I don't even have a Quirk!"

"Because you're my son, of course. But make no mistake, you absolutely do have a meta-ability – a Quirk," All For One corrected, shaking off his melancholy. "My own power allows me to sense those of others, and I believe it is only a matter of time before your Quirk emerges from its dormancy within you."

Izuku wasn't quite sure whether to believe him. "So it's true that you can steal Quirks? Is that why you kidnapped me, just to take mine?"

All For One snorted. "Yes, I can indeed take an individual's meta-ability. No, I will not and have never intended to steal yours. In fact, I wouldn't be able to take it even if I wanted to," he admitted. "My Quirk is powerful, but even it has a limit to what it is capable of doing."

Izuku tried very hard to reign in his rising curiosity, but he was unable to stop himself from asking at least a few questions. "A limit? How exactly does that work? How would it prevent you from stealing my Quirk?"

The supervillain chuckled. "You know, hiding the full extent of your meta-ability is practically a requirement if you don't want to attract the wrong sort of attention. Especially for someone like me." He leaned forward, patting Izuku's head in an annoyingly patronizing manner. "But it has been quite some time since I have had such a curious audience. Tell me Izuku, are you familiar with the term 'Horikoshi's boundary'?"

Izuku scowled and swatted the hand away. "It's a scientific measure for how strong your Quirk is, right?"

"Not exactly, although that is a common misconception. Let us start from the beginning, shall we?" All For One leaned forward, clear enthusiasm in his voice. "It has been two hundred years since the first metahuman was born, yet meta-abilities still defy all our understanding of the laws which govern the universe. However, there is one element which remains constant: Quirks always come with some sort of inbuilt protection for their user. Without this protection, it would be difficult if not impossible for most individuals to use their powers without harming themselves."

"Take Endeavor, for example. I'm sure you're familiar with him," the disfigured villain smirked. "His Quirk, Hellflame, gives him the ability to generate powerful flames along with intense heat. It also grants him impressive fire resistance, without which he would likely be unable to use his Quirk at all."

"Yet this inherent protection provided by our Quirks is not absolute. Horikoshi's boundary is defined as a ceiling, a soft cap beyond which whatever inbuilt defenses for the user are overwhelmed and they start to suffer increasing backlash from their own Quirk. In Endeavor's case, pushing past the Horikoshi boundary would mean producing flames hot enough to overwhelm even his formidable heat resistance. Other, less powerful Quirks often shut down after reaching this point. This phenomenon is often called 'Quirk exhaustion' by the general public, but it is more precisely a result of pushing too far past the Horikoshi boundary."

"In my case, Horikoshi's boundary manifests as a maximum number of meta-abilities I can hold, along with an inability to take Quirks over a certain level of power," All For One concluded. "Your dormant Quirk is simply too… heavy for me to take."

Izuku really wished he had one of his notebooks so he could write this down. "You said that all Quirks come with protection for their user," he observed. "But there's all those stories where kids end up hurting themselves when they first activate their Quirks."

"It is possible for young children with powerful meta-abilities to have a Horikoshi boundary so low that even a single activation of their Quirk is enough to cause damage to themselves. When Quirks first appeared, the point of meta-emergence actually used to occur at a much later age to offset this," All For One explained. "Although on average, the Horikoshi boundary for an individual was also much lower back then. I myself have first-hand experience with powers which caused significant harm to their users. Transformation types especially tended to have none of the safeguards you would expect from a modern meta-ability."

Izuku couldn't help but shudder at the implications. If someone with a powerful transformation Quirk like Ryukyu had been born earlier...

"Fortunately, there are methods to raise Horikoshi's boundary," All For One continued. "Rigorous training is probably the most common and widely known route. Any practice with your meta-ability will end up showing results over time, with additional improvements based on the intensity of the training."

"Oh, right! So is that why Endeavor always looks like he's on fire?" asked Izuku. "So that he's constantly training his Quirk?"

"You're partially correct. His fiery facial hair probably started as a means to train his Quirk control, but I believe Endeavor is very close to reaching the absolute limit of Horikoshi's boundary, what is known as the 'Tomohiro- Murata maximum'. The venting flames have likely been repurposed to help prevent his body from overheating." All For One snorted derisively. "A crude and garish method. Not unlike the man himself, really."

"I'm not sure I understand," Izuku admitted. "What's the difference between a boundary and a maximum?"

"Where Horikoshi's boundary is a soft cap, the T-M maximum is a hard cap to the human body's ability to tolerate the stresses of Quirk use. A plateau beyond which further improvement becomes practically impossible. Like Endeavor, those who train their meta-abilities extensively will begin to suffer increasing diminishing returns until they reach an upper limit at the T-M maximum."

"As meta-abilities become stronger, a point will eventually be reached where the human body is completely unable to withstand their power," continued All For One. "The average age at which meta-emergence occurs – at which children first manifest their Quirks – continues to trend lower even as the overall strength of their powers increases. You have already noted how there are an increasing number of stories where even the first activation of their Quirk inflicts serious damage to themselves. That is the basis for the government's infamous KDS, the Kaijin Doomsday Scenario, which is a cousin to the modern Quirk singularity theory."

Everything Izuku had read about the Quirk singularity theory said it was wrong, yet it seemed rather convincing when laid out like this. "Even if I believe you, it sounds like mankind is doomed. Is there anything that can be done about this singularity?"

All For One's sinister grin was almost visible through the mask. "Perhaps I'll show you, if we have the time." He stood up and stretched, Kurogiri instantly appearing by his side as though he'd been summoned. "Unfortunately, it seems my time with you has come to an end once again. I must admit, I've quite enjoyed our little discussion. I've not had such a good conversation in a very long time."

Izuku wanted to roll his eyes; he had mostly listened while the supervillain monologued. Although it was all very interesting, and he really wished he had one of his notebooks or something to write everything down in. He didn't look forward to trying to type up notes on his phone.

"I'll be back once again tomorrow," said All For One, as black fog once again shrouded his form. "Have a good evening, my son."

- End -

A/N: Hope the worldbuilding makes sense and is enjoyable. There's at least one more chapter of it to go before there's action again.

Thanks for reading, hope you enjoyed the chapter!