I. Accelerated Learning: Izuku’s Runaway Arc

I don’t want to start with what I think the quirk is. I think it’s more important to explain a few key story elements first, which will lead us naturally into the quirk’s nature.

In chapter 349, we got our most recent hint at what the Second’s quirk is.

“Faster!”

(Before you ask: no, I’m not gonna mention time travel.)

Izuku writes off Blackwhip and Faux 100% because he has nothing to swing from and the Gs from the speed would destroy his equipment. He starts to brainstorm ways to get to UA faster, but Second warns Izuku not to panic and make bad decisions.

It turns out, Izuku’s solution is to try using the Second’s mystery quirk. Somehow, this quirk is supposed to get him where he needs to go quickly.

This isn’t the only time speed has been mentioned in relation to the Second’s quirk. The last page of chapter 310 includes this panel:

Perhaps the semantics of the English translation are up for debate, because you could translate the Japanese version of this as “things will speed up” or “things will accelerate” among other options. But regardless, acceleration seems to be the theme.

So that’s it then! It’s Super Speed! Everyone go home!

...

Oh come on, that’s way too simple! And practically redundant given OFA and Fa Jin.

And so, I was reading Izuku’s solo arc as I mentioned earlier, and I found there is another instance of “speed” made in reference to the Second.

“Those who can match his pace and keep running alongside him.”

But wait, there’s more! In chapter 322:

“Everyone has always been way ahead of me...”

“I said you all couldn’t keep up with me.”

Do you find it interesting how quickly Katsuki rushes forward to catch Izuku? His leg is stylistically drawn to be practically invisible here.

Izuku’s solo arc is about his hurry to master OFA, but we see him demonstrate all the OFA quirks this arc except the Second’s. The implication is that it’s the only quirk he doesn’t have access to, that there’s something he needs to accomplish in order to unlock it.

We’re also told class 1-A all know what the OFA quirks are.

I believe the Second’s quirk is unlocked in the above page.

We have the Second’s narration of what Izuku needs to bolster himself superimposed over Iida rushing to Izuku’s side--superimposed over Iida holding Izuku’s hand.

Izuku then appears distressed and asks Iida to let go, but Iida refuses...while crying.

That last panel at bottom left? That’s the Second’s quirk.

I’m not saying it was activated though. I’m saying its activation conditions were met.

II. Holding hands gives you cooties

Katsuki knows what the Second’s quirk is, which is why he caught Izuku rather than took his hand. Izuku was shouting for Iida to let go of his hand because that’s how the activation conditions are met.

That’s why Izuku was on this solo journey searching for victims and villains to save. He was looking for people to clasp hands with, which would ultimately lead him to AFO and Shigaraki (you’ll understand how soon).

Now, is it as simple as holding hands? Just physical contact is enough, or the classic all-five-fingers-must-touch quirk factor type? I’m not sure. There could be one or two more conditions required. The first possibility? A connection of the heart.

AFO must know what the activation conditions are, so he’s built in fail-safes to guard against them. Three things happen in this scene that could all be the triggering event for AFO’s booby-trap, and all three could be necessary activation conditions. First: Izuku holds Nagant’s hand. Second: Izuku reaches out emotionally to Nagant, and she responds in-kind; Izuku reaches her heroic heart.

Third: Nagant says Izuku’s name.

The other potential activation factor is that both people who hold hands say each other’s names. Maybe only one person needs to say the other’s name. Maybe they both need to for it to work. I don’t know. What I do know is: Izuku had not yet spoken Nagant’s name before she exploded.

If this is indeed an activation requirement, it explains why AFO has gone to such lengths to hide his real name, why he gave Tomura a new name, and why he’s muddled his own identity such that even New Order wouldn’t work on him.

Remember how class 1-A were supposed to spend this day training to help Izuku master OFA? Katsuki’s moment of revelation in the above page is him noticing that Izuku intends to activate the Second’s quirk with Aoyama: Izuku reaches out his hand and says Aoyama’s name. And they’re both crying. It could be that crying is an artistic representation that their hearts have connected, or it could be that “connecting hearts” just requires them both to feel the same emotion at the same time; Iida and Izuku were both crying when they held hands in chapter 321.

And this means Aoyama probably was rigged by AFO.

Tsukauchi forbade Aoyama from taking Izuku’s hand and gagged him--so Aoyama would be unable to say Izuku’s name in response. They are preventing too many activation conditions from being met because they don’t know how many or which ones it takes to trigger AFO’s traps.

In chapter 321, Iida didn’t speak Izuku’s name, but he did say his own name (Ingenium) and referred to Izuku as a lost child. That may be enough to fulfill the requirement, or it may mean that all Izuku has to do is say Iida’s name now. Katsuki did say Izuku’s name, but does it count if it’s not “Deku?” Does it have to do with what that person’s name is to the speaker deep down? Did that requirement get met, and that’s why Katsuki didn’t take Izuku’s hand? Or did that not meet the requirement, but Katsuki catching Izuku met the hand-holding requirement? Perhaps that requirement is really just a physical touch requirement.

The super-fine details are muddled, obviously, but these elements are all clearly at play here, and that’s all we need for this theory’s purposes.

III. How did Yoichi Shigaraki discover he had a quirk?

Excluding how Izuku ate a strand of All Might’s hair, all artistic representations we’ve seen of the passing of OFA have been through hand-holding. I’m not saying each user activated the Second’s quirk at these times...unless that’s actually what they did.

What I am saying is that Yoichi didn’t know he had a quirk at first, and we all wanna know how he discovered his quirk seemingly by accident. Barring someone using a scanning quirk on him that tells them what his quirk is, there’s only one, plausible, non-convoluted explanation.

Someone else had a quirk that let them use Yoichi’s.

“What? Copy? You’re saying the Second’s quirk is Copy???”

No, it’s much worse than that.

Again, to preface, the finer details of exactly how this quirk works are still unclear, but I’m going to tentatively name this quirk based on the elements it must have.

The Second’s quirk at its most fundamental is...

Switch.

Swap. Trade. Exchange. Substitute. Whatever it’s called, it’s the power to (likely temporarily) switch one similar thing for another.

I say “likely temporarily” because if the Second used this quirk to trade quirks, he could only do it once if there’s no time limit to it. Their original state would have to revert and give him his real quirk back eventually in order for him to be able to use it more than once.

And as Monoma’s existence demonstrates, such a quirk would likely give the Second some intuitive knowledge of how to activate whatever quirk he ends up with. That’s how they learned what Yoichi’s true quirk was.

Maybe this switch quirk only works on other quirks. Maybe it works on something else. I can only say it must work on similar things, like an equal exchange of value, and actually I think it really is just that. It can swap any two things, so long as they are like-things.

This means there is potential that:

People could swap places

People could swap quirks

People could swap body parts???

Did you notice Second’s gauntlets hide his hands, maybe even prevent him from holding hands at all if he even has hands? I genuinely cannot confirm from the panels that he has hands anymore now that he wears two gauntlets. He only wore one when he reached out to Yoichi. Did he lose (give away?) his hand since then?

But gosh, AFO wouldn’t be able to steal a quirk that keeps hopping from person-to-person whenever Second used it, now would he? Or would he even be able to lay a finger on Second if Second could just swap his location with another person’s?

And I have to return to the DOES HE HAVE HANDS??? question because look at this series. Look at the state of Izuku’s arms. Look at how Chisaki now lacks hands (probably to keep Izuku from using the Overhaul quirk and become super OP for the final arc). Look at the noumu. Did the Second’s quirk inspire AFO to get into splicing? Is that why Shigaraki is growing so many hands--to use them as extras for the swap when he finally takes OFA and uses Second’s quirk?

And I want you to know that, in the above page, the Second speaks about making his allies into stepping stones.

This is just a guess, but I’m willing to bet that if one of the swapped items--let’s say a person--is destroyed (killed), the swap cannot revert.

If Second swapped himself for another person and then AFO killed the person who was swapped in, Second would be safe. He wouldn’t switch back to his old spot when the quirk reached its time limit--hence the panel of bloody spatters and implied human toll above.

The Second was in the position of choosing who would live and who would die.

What a nightmare AFO must have had trying to track this sucker down.

Reigning World Champions of Hot Potato.

IV. I Am Here

With the ninth generation of One For All, Switch has become something weirder.

One For All has been stocking up quirks, which means Izuku has multiple quirks to switch.

To tie it all together, I believe in chapter 349 Izuku is considering one of two things: swapping Blackwhip for Iida’s Turbo (which would leave Iida with Blackwhip and no communication to prepare him for the change), or swapping himself for another person to get closer to UA (but that’s a hard choice to make since Izuku’s currently over the ocean).

I think it’s about time I revive my old pet theory about the future of One For All.

“I am here.” All Might says it. But All For One says it, too. Except, in Japanese, they’re each saying something a little different:

All Might says “watashi ga kita,” meaning “I have arrived.” All For One says “boku ga iru,” meaning “I am here/I exist.” Izuku also says “boku ga iru.”

But...that last one can also technically mean something a little stranger: “[you] have me.”

We’ve seen how One For All’s stored quirks have been highlighted as inspired by and used in similar ways as others’ quirks, particularly those of his classmates. Izuku’s quirk analysis and synthesis skills over the series were always leading up to this point: the strategic exchanges of his classmates’ quirks.

But that’s dangerous, because he has no idea what’s happening where each of his classmates are. He doesn’t know if he’ll be able to wield any of their quirks with any degree of mastery. He doesn’t know if the quirks will mix together and make something even weirder.

He also has no idea if he’ll screw up using the quirk (see: the Second’s facial scar and the nebulous state of his hands).

Most importantly, he doesn’t know if he’ll swap for what he intends.

V. Plus Ultra Possession Theory

I said that one of Switch’s activation conditions could be a connection of the heart. I said that could mean the subjects must be in a similar emotional state.

I’m never gonna not bring up how AFO is interested in Izuku’s rage.

AFO explicitly plans to use Shigaraki’s hatred to steal OFA somehow. I’ve made so many, too many possession predictions to count at this point. Suffice to say, I’m convinced Shigaraki’s hatred’s gonna eat someone, and that someone may as well be Izuku, who has been warned time and again to control his damn emotions or else.

There’s a tiny special little section here in this meta about the relationship between quirks and personalities (which may be “hearts” for the purposes of this quirk theory, who knows). The point is, the canon has done its job to establish that quirks and personalities are related.

So, if Izuku starts swapping a bunch of unfamiliar quirks into himself, what will happen to his personality? His heart? His emotions?

Why have so many of the story’s themes centered around the notions of imitating those one admires or loves?

If Izuku loses control of his heart while overusing Switch, he’s gonna go fucking berserk. He could come to feel or know things others know. He could be torn apart by their feelings.

If Izuku loses himself to hatred, he could end up in an accidental swap with Shigaraki. Or, maybe it won’t be accidental. Maybe it’s a self-sacrificing gambit to save Tenko.

Maybe at some point Izuku Switches the quirks from OFA into AFO or Shigaraki, and that lets the vestiges fight AFO just as Star(s) & Stripe(s) did.

All Might’s vestige out here to haunt AFO’s ass forever.

Maybe Izuku is the one who ends up possessed through all of this, and we get a scenario similar to the ending of my Katsuki possession theory, only this way Katsuki is the one who has to connect with a lost Izuku.

I mean, who has a short fuse and explosive nature bombastic enough to overpower Shigaraki’s hatred?

Go get ‘em, Tiger.

VI. tl;dr

I believe the Second’s quirk is Switch.

The finer details of how it works or activates are murky, but at the very least it will allow Izuku to (probably temporarily) swap quirks with whoever meets the activation conditions. At best, it will allow Izuku to swap similar things for each other, which could even allow him to trade places with another person (hence he would become “faster”).

The activation conditions include some or all of the following: holding hands or physical contact, names spoken aloud, and an emotional connection/meeting of the minds/connection between two hearts.

The quirk can do batshit crazy things now that OFA is in its ninth generation, like swapping so many quirks around and utilizing Izuku’s amazing quirk analysis and synthesis skills foreshadowed since chapter 1. Some of these batshit crazy things could result in utter disaster, like, idk, facial scars and potentially missing hands.

Possession theory still strong, friends! Predictions galore!