After school, Izuku met up with Takeshi in the same place as always, and after their greetings, the superhero decided to start by asking Izuku a question:

"You know how some people have very dangerous Quirks, and yet it is very rare for them to hurt themselves by using them? Did you even think about why this is?"

Izuku thought about Bakugou and his explosions, and nodded "Yes, but I've never found anything close to an answer."

Takeshi nodded "It's understandable, because even I couldn't claim to understand that perfectly." He sighed "Even though it's one of the most studied subjects in the whole of power theory. But well..." He looked at Izuku "I understand enough to help teach you. Basically, you could say that at all times, Quirks are being subjected to two different influences, one internal and one external."

Izuku nodded, fascinated.

"The internal influence is clear. It is the will of the user. The same force that allows the user to be able to control their own Quirk, even things that don't have any visible physical means of control." Takeshi sighed "The external influence is something a lot more complicated. You can call it collective unconscious if you like, but that is not quite right. Essentially, it's a mysterious influence that acts upon all quirks to prevent them from 'breaking the rules'."

Izuku was confused, so Takeshi kept talking.

"For example: There is a hero who can create black holes. But they don't really act like actual black holes should act, and instead act more as some sort of suction and annihilation mechanism. This happens through a complicated process, as if there's something that takes the 'idea' of a Quirk and 'translates' it into something that fits while preventing it from causing too much havoc." Takeshi said "There are lots of Quirks that, in theory, could easily cause irreparable damage to the world. But in practice, none of them are capable of doing that, because of the restraints of that external force."

Izuku's mouth was open. This was something that made sense, but also led to countless other questions. What was that influence and what governed it? Takeshi had said something about the "collective unconscious", which was a good theory (most people in the world wouldn't like it if a Quirk randomly destroyed the earth, after all) but he also said it wasn't quite right.

The man saw that Izuku was thinking hard, and shook his head "You don't need to decipher everything all at once. Just be aware of that special influence for now. The other influence is far more important for you to think about right now."

"The individual influence, right?" Izuku said.

"Exactly." Takeshi said "That one actually involves something you should know about. What can you tell me about the Invisible Quirk Effect theory?"

Izuku thought a bit before talking "It's about how Quirk users, specially strong ones, are more resilient and recover faster than normal people, even when their Quirks have nothing to do with it."

"That's a pretty good summation." Takeshi nodded "But this theory is very flawed, if you know the right information." He clapped his hands together "Let's talk about the dawn of Quirks, where things were chaotic and confusing. A lot of research was done on the new Quirk users, and their tendency to be more durable than normal was noted even back then. There were lots of theories about it, of course. But do you know what was the most important part of those early researches?"

"What?" Izuku asked.

"The control groups." Takeshi said "By which I mean the Quirkless people. Their test results told us what being an "average human" meant. And more research of the type was done over time, and while it was so subtle most people missed it or thought it was a coincidence, after a certain period of time it became certain. It turned out that the Quirkless people were slowly becoming tougher on average, to the point where a normal person in today's world would be considered superhuman back at the dawn of Quirks."

"Seriously?" Izuku found it hard to believe.

"Yeah." Takeshi said "Now, this is partially speculation, but I believe it holds up due to how well it fits with other pieces of the puzzle that is Quirks. You know that despite frequently having biological explanations, Quirks as we know them wouldn't work if they were a purely biological phenomenon, right?"

"Ah, yes." Izuku said "The Unknown Energy Speculation, right?" He said the name of the theory he learned in school.

"Exactly." Takeshi nodded "Quirk users can access some external source of energy in some fashion, regardless whether it is an extra-dimensional phenomenon, some mental thing like the collective unconscious I mentioned before, or even something like the soul... It is definitely there, and the age of Quirks must have begun when the humans were granted access to that source. And that leads me to my theory."

Izuku paid extra attention

"What if everyone could access that external energy, not just people with Quirks?" Takeshi asked "What if the sudden accessibility of that energy was the thing that actually started the age of Quirks? That would explain a lot of things, wouldn't it?"

Izuku kept listening, fascinated.

"What if Quirks simply make it easier for the user to access that energy, and that's why people with Quirks would be naturally stronger, since they would toughen themselves up subconsciously? What if seeing people with Quirks that are tougher even if their Quirks don't involve that made Quirkless people subconsciously access that same energy and toughen themselves up due to believing that was just normal?" Takeshi looked incredibly excited to be talking about it, but then he sighed.

"Like I said, a lot of that is speculation so you shouldn't just take what I'm saying as gospel." He spoke carefully "Still, it would certainly explain a lot of things, including the many reports throughout history about quirkless heroes accomplishing superhuman feats."

Izuku nodded.

"The most important part of that in regards to you is that you must be aware of that energy, because you will need to manipulate it at a very precise level if you want to be able to develop strong skills." Takeshi concluded "Now, the next really big secret that you must keep in mind is the following: Every single Quirk works by either manipulating particles, or waves. Never both at once."

Izuku started to nod, but then he realized something "Is that really true? It doesn't seem right."

"Yes, it is." Takeshi said "That's one of things I am the most certain about, given how All for One works. A lot of Quirks do things like manipulate particles to generate waves, or release waves to manipulate particles, so they can affect both, but the origin of the effects is either one thing or the other."

"But what about Quirks involving light?" Izuku asked "Light is both a wave and a particle, right?"

"That's a very good question." Takeshi praised "The short answer is that both apply separately. Some quirks interact with light as if it were a particle, while others do it as if it were a wave." He raised a finger "However, there is a lot of research being done on light based quirks, because they borderline break the rules of the system." Takeshi seemed to struggle to find the right words "Basically, even though the rules of limited manipulation still apply to light based quirks, there are some phenomenons caused by them that can't be reasonably explained with that."

"Right... So the world of Quirks is really complex, isn't it?" Izuku said.

"Indeed." Takeshi said "Do you have any other questions?"

Izuku thought for a moment "You said All for One works by manipulating particles, right? Then does that mean that I'll only be able to imitate Quirks that are based on waves?"

"Surprisingly no." Takeshi said "All for One works based on results instead of causes. Like I said, that are many particle based abilities that end up manipulating waves, and while you can't imitate the origin of the ability, you can still imitate the manipulating waves part of it." He stopped for a moment "From my experience, most abilities have at least one aspect that you should be able to copy, so don't worry about it."

"Understood... Then, I guess I can't think of anything else to ask right now." Izuku said.

"In that case..." Takeshi grinned "It's time for us to deal with the matter of your physical training."

Izuku gulped.

+0+

And then Takeshi brought Izuku to... a fitness center.

The boy felt a faint sense of disappointment for some reason.

The two got in and Takeshi spoke with the people in the front desk for just a bit before they were allowed to enter and go into a specific room, where the person Takeshi had requested was waiting.

She was a woman whose very appearance screamed "personal trainer", with short black hair and a body with well defined muscles. She introduced herself as Haruka Atami, and Izuku felt shy due to how attractive she was.

"So he is the one you want me to train?" She asked Takeshi.

"That's right." Was his answer.

"What's the goal here? You mentioned a ten-month training program, so that means you must have an objective instead of simply getting this boy in shape." Haruka said.

"It's simple. During this ten months, the goal is to train him to the standard of an Olympic athlete." Takeshi explained.

"Are you serious about that?" Haruka asked, incredulous "That would be an extremely tough and demanding training schedule."

"Yes, I am serious." Takeshi confirmed "Izuku here is not going to give up, and he will complete whatever training menu you have for him."

"Oh, really... If that's the case, I think it would be interesting to do something like that. How much free time he has?"

And the two started getting into details as Izuku felt like Takeshi was throwing him to the wolves. He swallowed his worry, knowing that the path to becoming a superhero would be very tough.