A/N: First part is a flashback don't get too confused! Enjoy this chapter. And remember to take breaks and drink water.

SLIGHT SPOILER WARNING! HISTORY/BACKSTORY OF ONE FOR ALL.
That's all, enjoy!

Izuku POV:

—THE DAY BEFORE—

"Can we talk in private?" I ask.

"Yeah, of course." Mirio smiles as we walk a little.

"Okay... when I was taken by All for One he said he was going to give me quirks, so I could defeat All Might's successor. And things started to make sense... Nana Shimura was All Might's mentor, and they had very similar quirks." I clear my throat.

"Correct me if I'm wrong, All Might has the ability to pass down his quirk and he passes it down to you. You're All Might's successor." I turn to Mirio.

"You're pretty smart Izuku... I don't think I could lie to you since you have every little detail down about the story. Yeah I'm All Might's successor, but that has to stay a secret." Mirio speaks slowly.

"I won't tell anyone!" I reassure him.

"Thanks." Mirio sighs.

— CURRENT TIME—

   Sir Nighteye asked to see me during lunch. I wonder if I missed some paperwork I have to do because of the Nomu attack and Stain. I inform Shinso and Hatsume that I can't join them today then I head to the room I was directed to.

"Ah, Izuku, there you are." Sir smiles and shakes my hand.

"It's nice to see you again Sir." I smile back.

"I've been informed that you might know about All for One and One for All." He says, leading Mirio and All Might into the room.

"One for All? Is that what Mirio and All Might's quirk is called?" I ask.

"Yes it is." All Might answers.

"I'm certain young Mirio told you that this must be kept top secret." All Might looks at me.

"Yes he did say that, I swear to never tell a soul!" I promise the heroes.

"I'm glad to hear that, but if it's not too much trouble, can you remember anything All for One might have told you?" All Might asks me.

"I- All for One only spoke about how he would give me quirks to help defeat All Might and his successor. He said he would start off by giving a warp quirk and then some doctor would give me the rest..." I mutter.

"The doctor, did he give you a name?" Nighteye asks me.

"No Sir, he told Shigaraki to take me to the doctor and that he would finish the rest." I answer.

"I see. Thank you Izuku, you've done a lot for us. But are you certain that you don't know anything else about this doctor?" Night looks at me.

"Well, he's probably they guy who built all the Nomu machines and the machines that All for One was wearing... but I didn't hear anything about him, sorry." I rub my neck.

"No need to be sorry Izuku! You helped us when you didn't need to, so thank you. And sorry if we made you remember anything you didn't want to." Mirio ruffles my hair.

"It's okay." I give him a smile, that needed a bit of forcing.

   After the talk about All for One I went back to class. I can't help but feel like I'm involved in something much bigger than I know. So I have to find out more about All for One and One for All! I should start in the library after school.

"Show me what you have so far, Izuku. Let's try to think of a move that you can use in the provisional licensing exam, unfortunately they don't allow guns and any uncleared weapons." Ectoplasm tells me.

"Right! I'll have to think a little harder on how to pack a punch without my gear, good news my gauntlets are still in the game. So let's give this a try!" I run towards the copy of Ectoplasm.

   I fake a punch and pull out at the last second, sweeping my body under the copy and smacking him into the floor. I take his arm before he can recover and slam him once more into the ground, using the gauntlets full force.

"Your strength and speed are remarkable Izuku, now let's run it again but watch your stance. At one point I saw an opening to tip you over. So keep an eye out for flaws." Ectoplasm creates another copy.

"Yes sir!" I get ready to do the move again.

   I practiced a few moves with Ectoplasm for the remainder of class. After class I went straight to the library and pulled out a few books. I grabbed a book on historic battles in hero society, another book about quirk and quirk family trees, then one on All Might's past. I'm certain I've already read through the All Might book before but I might as well revisit it.

   I took the books back to my bedroom and grabbed an empty notebook. If I get notes it could be dangerous to leave them out in an easy to lose or steal notebook. Good news, since I've been taking notes on heroes for a while now I've made a code for certain things. Like a different language of sorts. So I take all my notes in my code.

   I start off with the book on quirks and quirk family trees. Most notable things inside were about the second generation of quirk holders. There was a strange amount of powerful quirks and quirk bloodlines that went missing, like they ceased to exist. It must have been All for One. With an ability to steal quirks he must have been stocking up on quirks. Most notably he took strength quirks, healing quirks, and travel quirks. A powerful family stopped having a quirk called warp gate. With its description it sounded exactly like Kurogiri's quirk. I take note of that.

   The next book is about All Might's history. Just like I thought, I've read this book before. But I still note his teacher, Nana Shimura. There's hardly anything said about her or her death. Just that a villain killed her and left a legacy for All Might. I'm certain it was All for One though. In an effort to end One for All as a whole, he had to kill Shimura before she could finish training her successor. We were all very lucky that she had already passed down the quirk to All Might, otherwise nothing would have stopped All for One from ruling all of Japan. I make note of everything I can about Nana Shimura and her two quirks.

   Finally I start on battles throughout hero history. This is where I found some really interesting stuff. I knew All Might had fought All for One, however I thought he killed him and gained the injury to his stomach. I thought that was why he started to do less hero work but it looks like All Might and All for One could have battled quite a few times. More than that it looks like One for All, the quirk, has been held by many people. It started during a full out war with none other than All for One's brother, Yoichi Shigaraki.

   Yoichi had an illness that kept him from being nearly as strong as normal people and he was thought to be quirkless. During an argument with his brother, All for One forced a strength quirk on to his brother, unaware of Yoichi's true power. Yoichi wasn't quirkless and was able to pass this power down by giving his DNA to a friend of his. The friend goes unnamed but I take note of Yoichi and his entire life.

   I decided to go back to the quirk book and read through different documents of strength quirks and how they worked. I was able to find out that before All Might there were seven holders of One for All. It starts with Yoichi Shigaraki, then an unnamed holder, then another unnamed user, then Hikage Shinomori, who passed the quirk to Daigoro Banjo, then En (with no family name), and then Nana Shimura. So many people who owned One for All but I noticed a pattern.

   Even the people who didn't fight All for One, who still held the quirk, died early. After looking and looking again I came to an unfortunate conclusion. These people died early because they already had a quirk of their own. All Might didn't die at thirty because he was born quirkless. But Mirio has another quirk already. Permeation.

'I have to tell Mirio!'

"Izuku!" There was a knock at the door.

"If you ever get done studying, dinner is ready!" It's Shinso.

"R-right here I come." I close the books and hide my notebooks under my bed then join the rest of my class downstairs for dinner.

   I'm not sure how I'll tell Mirio but I know that I have to, his life could be at stake! I can think of a way to tell him tonight, so I'll talk to him tomorrow. If I get a chance.

A/N: Hope you liked this chapter! It was 1535 words!