Summary: How to jumpstart your elder hero with performance issues!

Chapter 47: I-Island (Expo Day 3)

Aside from the meeting with Star and Stripe, the first two days of the I-Expo had been mostly business. Given their own recognized expertise in Quirk Energy Theory, Izumi and Momo couldn't avoid giving a few lectures and attending some seminars and round tables on the topic. Likewise, there was some limited dealing for Aegis to be done. Truth be told, the Expo wasn't as heavily used for business dealing as one might think. Oh, It was primarily a place to brag, make the public aware of things exciting things that would be coming down the pipeline for them to buy into in the future, and awe said public with all the cool stuff. A few boring 'parties' would see serious business discussed, but they were more the sort of thing the Yaoyorozu Group handled, not the privately-held Aegis Inc. Despite that fact, there were always at least a handful of new deals to at least get the ball rolling on, typically related to whatever new reveals had been made. Izumi and Momo had gotten off lightly this time, since the most interesting new developments were firmly in Melissa's area, and they'd cheerfully thrown her under the bus as a 'learning experience.'

As a result of Melissa's unwilling sacrifice, aside from a need to attend the I-Island Gala that would finish off the Expo, Izumi, Momo and 2B were able to get free from their business obligations by day three. Which was good, as they were now attending a pre-planned meeting of another sort. David Shield was in attendance, despite this being an Aegis Inc lab facility, and All Might was looking extremely confused about why they'd all ganged up on him to collectively drag him into said lab. Momo, as both his direct successor and arguably the most charismatic of those present, was the one to get the ball rolling on an explanation for their mentor.

"So! We've invited you here today, All Might-sensei, to deal with the issue of your diminishing reserves of One for All."

Toshinori, in his regular form despite Momo calling him All Might, straightened in alarm as he looked at…David Shield. Momo and Izumi sighed, Izumi taking over to take the blame for this bit.

"Yes, we informed David about One for All. In truth, we'd assumed you'd already told him. He's literally the world's greatest expert on Quirck Energy Theory, with only 2B, myself, Momo, and his daughter being even in vague shouting distance. Given the nature of One for All, you not availing yourself of his expertise, particularly after your injury, wasn't something we'd even considered. We quickly realized our mistake, of course…but went ahead with our plan and told him anyway. Whatever your reasons for not doing so, we've worked with him before and felt able to trust him with the information. Our current assumption is that you may not have told him because of Melissa?"

All Might winced, sighed, and slumped.

"No. That was a contributing factor later on, after I started looking for a successor. But the original reason was much more pedestrian. My partnership with David happened while I was, effectively, in hiding from All for One. At that time, I had personally told no one. All those aware of One for All had been made so by my predecessor, not myself. Something that didn't change until after I returned to Japan and began my assault on All for One's operations. After that, David and I were rarely in the same place at the same time, and it's not information I've ever been willing to reveal any other way than in person. Especially not on I-island, with all its monitoring?"

David, who'd been looking a little tense at the start, had slowly relaxed as the explanation. He even nodded at the last bit, answering the implied question at the end.

"That sadly makes sense. Though you needn't worry about that monitoring here." His voice turned wry a moment later as he gestured at 2B. "For some reason, Aegis Inc has always been able to keep I-Island security out of its affairs."

His dry tone was met with a very smug smile from 2B. Which only made him chuckle ruefully.

"Regardless of understanding your reasoning, I'm glad Izumi and Momo reached out to me. Not just for your sake, but because I must admit I was in the process of developing something to try and help you. My solution would have been a bit of an…extreme, had I finished it. Given that it was almost finished, their timing was fortuitous, as that particular genie is best left in its bottle. Thankfully, once fully aware of the reasons why you were growing weaker, I had that project sealed. Instead, I've been working with these two young geniuses via secure HSN channels to solve two problems with one bullet, so to speak."

Toshinori looked like he very much wanted to ask about that sealed project. Instead, likely knowing his old friend wouldn't say anything about it even if asked, he focused on the second part of what David had said.

"Two problems? From what Young Yaoyorozu said, I assume my diminishing embers of One for All are one issue. But what is the other?"

Momo, clearly glad her mentor wasn't upset at their brining his old friend into the loop, pounced on the topic change the instant it was offered.

"Well, technically speaking, One for All is killing me. Though we've been managing the issue."

All Might snapped upright, eyes wide as he pinned Momo with an intense expression that made her go on very quickly.

"Ah…that probably sounded worse than it could have. It's less that it is directly killing me, and more that it, unmanaged, was accelerating my aging. You have, of course, seen what happens to the Nomu. I'm assuming you've guessed, or even know from previous experience with All for One, that some of their issues are caused by their multiple Quirks?"

All Might frowned.

"Yes. There seems to be an unknown limit on how many Quirks a person can have. Though that limit doesn't always appear to be the same, and we never figured out a pattern."

Izumi nodded and reached out to tap a control that brought a hologram to life on the table between all of them. It showed a human silhouette and several side bars.

"Right. Well, as it happens, Momo and I realized almost immediately what was going on. A Quirked human is genetically distinct from a baseline human, having developed the ability to process and generate the ambient Quirk Energy Field of the planet. The difference in strength between older generations of Quirk Users and newer is mostly due to the difference between merely harnessing and actually generating QE. The first generations only processed and refined the ambient energy. Current generations often generate at least some QE of their own. A natural, if somewhat accelerated, progression. Presumably the speed of the adaptation was made possible by the reality-fuzzing properties of QE itself. A minor blessing, despite the chaos Quirks caused for the world, as unadapted humanity would have died off from toxic effects of QE without the adaptation."

She began manipulating the hologram as a visual aid as her explanation continued. One silhouette became two. The first showed arrows indicating QE flowing into the body, to a small reservoir, then being emitted as a Quirk. The other showed both QE flowing in, as well as a dynamo generating it internally. Notably, the reservoir for the second was much larger than the first.

"Every person has a sort of threshold, however, depending on how far along that process of adaptation is for them. Generators have the highest thresholds, as a general rule, as their body has to deal with both variations in ambient QE and stockpiling of its own continuous generation. Essentially, every Quirk has a reservoir similar to One for All, only without the stockpile aspect which makes One for All retain QE almost entirely. Most people, when their reservoir is 'full,' cease taking in any additional QE. One for All, on the other hand, never stops. The Quirk itself stores all the excess energy as effectively a second reservoir which can expand infinitely."

The figures were replaced by others, this time showing a count of Quirks.

"The issue is that people aren't supposed to have multiple reservoirs. Technically, having the reservoir itself is utterly harmless. Indeed, this is presumably how All for One can hold so many Quirks. The reservoirs don't cause the problem. Active throughput, however, does. Someone with a dozen passive Quirks will start having problems fast, because those reservoirs are all active, all the time. All of them generating conflicting QE waveforms. The results are obvious in the Nomu and their mutations."

Izumi gestured to one figure which began mutating as passive Quirks were added. The other figure, now with a cartoonish face, was gaining active emitter Quirks and grimaced when it activated more than one. It showed active pain when trying to activate several at once.

"You avoided the problem entirely. Despite being born 'Quirkless,' you are genetically a Quirked human. There's basically no one left that isn't since that part is an environmentally caused mutation. You simply didn't express the ability to use the energy in some fashion. This meant that when you got a new reservoir with the means to use it, you were able to use it without consequence, as there was no competing waveform of QE. We've tracked down previous users of One for All and discovered that the only poor bastard with a passive, always on, Quirk aged horribly prematurely as his body struggled to handle Quirks with very different waveforms in the same body."

Izumi leaned back even as Momo leaned forward to take over the explanation, leaving the hologram displaying the last known image of Hikage Shinomori. The poor bastard looked twice the age he was listed as in the image.

"When we initially realized what was going on, we were not particularly concerned. While my Quirk does have passive mutations, they aren't active effects. Which meant that I only experienced accelerated aging while actively using both One for All and my own Quirk. Better yet, since my Quirk's waveform is incredibly flexible, due to essentially being a type of raw energy manipulation, I was impacted far less seriously than most people would be. It did get us looking more closely, however, and we eventually discovered that the conflicting waveforms is only one part of the problem. The other part is…less easily avoidable."

Momo delicately tapped a key on the controls for the hologram. This time, a full breakdown of the QE in her own body was shown. It was a medical diagnostic version of a Hero Scouter's QE scanner. Far more comprehensive…and it showed the problem for those that knew what they were looking at. All Might most likely didn't, so Momo explained.

"What you see here is essentially a map of QE Stress. That is, how tolerant a body is to the flow of Quirk Energy. My own quotient is, thankfully, extremely high due to how energy-intensive my natural Quirk is. Even so, One for All has grown to the point that it is a generator Quirk as well as an absorber. As such, even passively holding it, is placing strain on my body, as I generate more QE than my body can handle. This is the exact thing that the human body developed QE absorption properties to deal with in the first place. If it hadn't, and if the field of QE that developed here on earth were stronger, it might have done something extreme to a human encountering it. Like, say, slowly causing chlorination of their body's cells, effectively turning someone into a pillar of salt."

All Might blinked, gaping at that comment, even as David Shield chuckled. He believed that was an extreme case, not being aware of WCS, and they'd never corrected him. In fact, from the data 2B had on White Chlorination Syndrome, it was literally what would have happened if humanity hadn't adapted quickly enough. What had happened to humans in her original reality, in point of fact. The Maso field there had been almost twice the strength of the QE field here, and humanity's ability to adapt had been overwhelmed.

"My case isn't that bad, obviously. Better yet, QE Stress Tolerance is something that develops like a muscle. If I were only getting the passive effect of having One for All in my body, there wouldn't be an issue at all. Unfortunately, I have a powerful QE generation effect of my own…and the individual Quirks within One for All may have generators themselves. If we hadn't done anything about it, I would currently be experiencing low-grade constant pain, as if my body had a nasty bacterial infection."

All Might was pale at this point and opened his mouth to ask a question. Momo cut him off with a smile and raised hand, however.

"No, that isn't currently happening. Don't worry, we found a stopgap solution immediately, one which has been slowly allowing my body to adapt to the strain. Even using only the stopgap, within three to four years I would have adapted to the point it was no longer a risk. The nature of that stopgap solution also presents an opportunity, however. Which is why you are here."

All Might breathed out a slow sigh of relief, slumping and closing his eyes for a few moments. They let him absorb for a moment, and he eventually nodded.

"Okay. That…its more than a little terrifying that I never had any idea and could have seriously hurt you just by giving you One for All. I assume this all loops back around to my diminishing stores of One for All somehow?"

Momo nodded, relieved to be over the worst of it. She smiled excitedly as she took up the explanation again.

"Right! The reason why you are slowly losing One for All is because you lost its generator in the transfer. You're actually still passively absorbing QE, which is keeping the embers alive to an extent. But that's not enough to maintain One for All. The powerful generator it had developed is what makes it seemingly inexhaustible, after all! So long as even the embers remain, however, you still have a reservoir for it, and it can theoretically be refilled! The, uh…problem with that is a QE compatibility issue. Which is why we needed Doctor Shield's help."

David Shield waved, smiling as All Might looked to him. He shook his head in bemusement as he took up his part of the explanation.

"In truth, they likely could have sorted it out on their own, given time. Aegis, after all, is the company that figured out how to store QE at all. Even if only in a very limited fashion, so far. The problem they had was that they've only ever been able to store a single waveform of QE, which meant it was only really good for temporarily storing a reserve of someone's own Quirk Energy. Even then, the way it was stored would denature it to neutral QE eventually. Which is toxic when pumped back into someone too fast for them to natural absorb. Well, into humans, at least."

Shield grinned and pointed at 2B.

"They failed to mention that 2B is their stopgap. She's a Quirk, not a human. Better yet, she's one that can natively absorb QE even after it's been natured by someone Quirk. Though the farther it is away from baseline, the less efficiently she can absorb it. If Miss Midoriya tried to help directly, the dual nature of the waveform would poison her. But having 2B manifest and leech the excess QE out of Miss Yaoyorozu's system through physical contact, keeping her under her maximum stress load, has been preventing anything bad from happening. Miss Yaoyorozu's system is still being pushed hard, but only enough to cause expansion rather than damage."

2B nodded stoically. But she also spoke up to point out their problem.

"Unfortunately, trying to release that energy back into you, All Might, would have created toxicity from either Momo's Quirk Energy if we did it directly. Or else similar toxicity if I did it, since it would have been denatured into base QE."

David nodded acknowledgement of that, before continuing to explain his part.

"What they didn't know how to do was to tune QE to another waveform. Or at least filter it. They had gotten at least momentarily stuck and consulted me…only to discover that I actually already knew how to do that. Indeed, it had been the core discovery I'd needed for the dangerous prototype I was trying to make. With each of us having a piece of the puzzle, it actually wasn't that hard to create a solution."

Momo, filled with bouncy energy now that they were at the big reveal, practically lept to a piece of equipment previously covered by a tarp. She whisked it off, revealing…two completely ordinary leather recliners with a large QE capacitor, a pair of cuffs akin to those used to measure someone's blood pressure, and a sleek computer display. Proudly, Momo introduced the fairly tame looking device.

"May I present! The world's first Quirk Energy Transfuser! So long as it has a sample of two people's Quirk Waveforms, this device can transfer excess QE from a donor to a receiver! Efficiency currently sucks horribly for people with drastically different Quirks…but both of us have One for All. Meaning that I can transfer excess One for All energy that is harming me back to you. In doing so, we get the bonus of it refilling some of your reserves, extending how long you'll be able to retain One for All for!"

Despite always finding bouncy Momo adorable, Izumi was quick to make a clarification.

"This won't do much for your time limit. Sorry, All Might. That's related to your injuries rather than QE levels and we're still working on solutions for said injuries. But it does mean you won't simply run out of the embers of One for All. Which will mean you should be able to stick around teaching at UA until Momo is ready to graduate, easing the transition between your era and hers."

Toshinori Yagi looked completely blown away as one of his biggest fears was preempted by a pair of teenagers and an old friend. One he was now seriously kicking himself for not having consulted before…

... ... ...

A/N: So, strangely, this isn't really a Quibble I have with the canon series. But I do wish the author had addressed some reason why they couldn't just transfer One for All back and forth between Izuku and All Might whenever All Might started running out of embers. If I understand the Quirk right, even holding it for a few minutes would have replenished All Might's stockpile, while Izuku can't even use the thing at Full Power in the first place. It seems the obvious solution to keeping All Might going until Izuku was ready? Still, it's not that big a deal for me. Here, though, with Izumi/Momo/2B being so much more knowledgeable about Maso/Quick Energy? It seemed silly that they couldn't have come up with a solution to at least that part of All Might's issue. He's still on a time limit, since this didn't address his injuries. But that time limit isn't shrinking just because the embers are going out, at least.