As Izuku stepped out of the convenience store, he double-checked his shopping list to make sure he had everything he needed. Class 1-A was throwing a small party to celebrate defeating Class 1-B in a practical exercise. It had started as a joke because Monoma had thrown a party the last time Class 1-B had won, then Katsuki had screamed his class would have an even bigger party next time. Mostly it was an excuse to hang out together. Class 1-B had already stated their intention to crash the party, and Kendo had promised to keep Monoma under control.

Izuku and Shouto had been assigned to buy snacks and soda. Different people had added their own favorite types to the list. Izuku's bag had ginger ale, Coca-Cola, potato chips, and popcorn. He glanced over sideways, wanting to check Shouto's bag too. But maybe that would be rude. Maybe it would look like he didn't trust his own friends. Or maybe he was overthinking it because he had anxiety.

Shouto held up his plastic bag. "Here, check mine too."

He'd definitely been overthinking it. Izuku leaned over—and a pair of gloved hands wrapped around his waist and yanked him backward into a white van. His bag slipped from his fingers.

Izuku had a split second to act. His body moved on its own. Alas, his body made the mistake of rescuing the soda before it hit the ground. In that wasted moment, his attacker fastened a sweet-smelling cloth over his mouth. Izuku recognized Tomura Shigaraki's badly bitten nails and archer gloves before the chloroform knocked him out.

Izuku woke up surrounded by steel walls. From metal door and whirring ventilator, he must be inside a bank vault. He immediately summoned One for All, but the green sparks did not respond. The cuffs tying his hands behind his chair must be quirk-suppressants. He jerked his head in all directions.

A long table sat before him covered with a white cloth. To his right, Shouto was cuffed to an identical steel chair.

"I'm glad you're awake," Shouto said, fidgeting in his bonds. "I'm sorry, they threatened you to force me into the van."

"That's not your fault," Izuku said firmly. "I'm the one who carelessly got caught."

"But they later said they wouldn't have harmed you, so now I feel stupid," Shouto said.

"That's right, we won't harm you." Tomura Shigaraki stepped into the room, without his customary severed hands. Instead, he wore jeans and a sweatshirt reading: I like gaming and maybe five people. Dabi followed, in a dark trench coat and ripped jeans.

"Because we're hostages or your next villain recruits?" Izuku demanded.

"Because you're my little brother." Tomura attempted a smile. It looked a bit off on his face.

Izuku stared, trying to assess if the villain was more or less dangerous now he'd completely lost his mind.

Shouto gasped. "Tomura Shigaraki is All Might's secret lovechild, too? Shocking!"

"Absolutely not." Tomura recoiled. "Midoriya—I mean, Izuku—is All for One's son. I can't understand why Sensei hid his family from me, his adopted child. When I had nightmares crying about Hana's death, Sensei told me to get a replacement for her. That must have been a hint. Clearly if Sensei wasn't locked up in Tartarus, he would want me to become your new older brother. Welcome to the family, Replacement Hana."

Leaning over, Izuku hissed to Shouto, "This had better not be one of your conspiracy theories that somehow crept over to the League of Villains."

Shouto replied, "Nonsense, Dadmight is the only theory for me."

Not listening, Tomura continued, "Dabi came up with the conspiracy theory about my sensei being your father. I didn't believe him at first, but the evidence kept piling up."

Izuku turned his glare on Dabi. "Then this is your fault!"

Tomura shook his head. "I can't believe Sensei didn't tell me about my cute little brother sooner. We'll have to make up for lost time."

Izuku's laughter had an edge to it. "Don't be ridiculous. My father is an ordinary salaryman working abroad in America. He's insanely boring and mediocre. One might even call him forgettable." No matter what, Izuku refused to accept All for One as a father. Even if he had to go to America and track down his disappeared dad personally!

"I know this must be a lot to take in." Tomura tried to pat Izuku's head. He barely withdrew his fingers in time to avoid getting bitten. "But I'm going to need you to adjust quickly so that I can win the Big Brother Contest against Dabi."

Izuku's eye twitched. "I'm sorry, I thought that you said you were holding a big brother contest with me as your little brother, but I must have misheard you because that would be stupid." With great effort, he restrained his temper. A hostage should stay calm and negotiate. He swallowed and tried to control his tone. "What does Todoroki have to do with this? He's an uninvolved party. Let him go, and I'll cooperate."

Shouto made a pained noise. "I won't leave you—"

Izuku kicked his chair and hissed, "You need to tell everyone where to find me."

Tomura rubbed his head. "It's a bit of a long story. After I found out about you, I decided to become the best big brother from now on. Dabi started bragging about being a better older brother than me because I'm an amateur. Naturally, I must prove him wrong so now we're holding a contest for the best big brother and you two will judge—"

Izuku interrupted, "I still don't see what this has to do with my friend. Especially because your conspiracy theory is bunk!"

Shouto nodded. "Yeah, you're ignoring all the massive piles of evidence for the All Might lovechild theory. How do you think Midoriya got the same quirk as All Might? It's not as if All Might could give away his quirk!"

Izuku insisted, "I can judge the contest alone (you both lose.) Why do you need Todoroki?"

Dabi struck a pose. "Because my real identity is Touya Todoroki!" He poured liquid over his hair. As his locks turned white, he spun in a circle and did a little jig. "I rose from the grave to take revenge on Endeavor!"

If Izuku's hands had been free, then he would have face-palmed. "So you're both delusional. Wonderful. Just wonderful."

Shouto said, "Actually, he's the real Touya."

"Seriously?" Izuku blinked. "Are you sure? White hair doesn't prove anything. Ever since the dawn of the age of quirks, Japan is full of people with naturally white hair."

Shouto said, "Only my family dances so awkwardly, like a swan trying to ride a bicycle. It reminds me of my father dancing on the table when he gets drunk. That can only be Touya."

"Huh. Well, I still don't have any connection to All for One," Izuku mumbled.

"Hey!" Dabi yelped. "How dare you compare me to Endeavor?" He started to reach for Shouto's throat, then stopped. "Um, I'll forgive you because we're so close. We see each other all the time. I regularly tell you how much I love you. You adore me. Right?" He winked frantically.

Shouto stared in confusion. "I haven't seen you since you died. How did you come back to life, anyway? I need to know for my conspiracy theories."

Tomura pointed and laughed. "Dabi, I knew you were lying about having a close relationship with the hero kid! As if a selfish guy like you could ever be a proper big brother. You don't even care about him."

Dabi scowled. "Of course I adore my little brother. Just because I haven't seen him in years and tried to kill him once doesn't mean I don't love him. That's how brotherly relationships work, you amateur big brother."

Shouto gasped. "Now I recognize you! You're that racoon-like creature who sneaks into our house regularly to do your laundry and steal our food."

Izuku winced. Just how bad was the security around the number two hero's house, if a villain could regularly break in?

"See? We're close." Dabi nodded. "And we're about to become even closer." His clenched fists did not match the fake smile on his face. "Shouto, I'll give you anything that you want if you say that I'm the best big brother."

"Will you let Midoriya go?" Shouto asked.

Tomura spoke first: "No."

Shouto bit his lip. "Then can I have a bowl of soba? I got hungry while you left me tied up inside a bank vault."

"Done!" Dabi ran out of the vault.

"Hey!" Tomura cried. "Why does Dabi get it so easy?"

Shouto shrugged. "My family has left my standards so low the bar is located somewhere in hell."

Tomura turned to Izuku. "What bribe do you want to call me best big brother?"

"What nonsense is this?" Izuku demanded. "You have me handcuffed to a chair. Even if I said you were the best brother, I'd be lying to appease you. And for the last time, we're not related because All for One is not my father! The only thing I want is to get out of these handcuffs!"

"I can't. Then you'd run away," Tomura said. "Sensei taught me that all younger siblings must be immediately locked in a bank vault for their own protection, especially if they have any heroic tendencies. If I let you go, then you would abandon me, start a legacy of heroes dedicated to my destruction, then die a heroic but pointless death."

Izuku asked, "Will you uncuff me if I promise not to leave without punching you in the face first?"

"No." Tomura fiddled with his gloves. "Do you want money? Power? All the video games you can play? All the delicious food you can eat? Your enemies' severed heads? Hmm, what would a hero brat want… Do you want hero merchandise?"

"Noooo…is it All Might merch?" Izuku asked. The words leapt out of his throat before he could stop them.

Tomura's eyes lit up. "I do have some of that." He left the vault, too.

Now the villains had left them alone, Izuku turned to Shouto, about to start planning their escape. Unfortunately, Dabi chose that exact moment to return with a bowl of cold soba.

Shouto's eyes widened. "You remembered that I liked my soba cold. Awww! You're such a good brother."

Dabi nodded. "I knew being too lazy to microwave my leftovers would pay off." He placed the bowl on the table.

Shouto said, "You're going to have to uncuff me to let me eat it."

Dabi snorted. "You think I'm gullible?"

"I wouldn't leave without Midoriya. It's uncuff me or handfeed me."

Dabi shuddered. "Point taken. Promise not to attack me on how much we both hate our father?"

Solemnly, Shouto nodded. "I promise."

Dabi pulled out a key ring. Izuku carefully noted that the villain kept his keys in his back packet.

After being untied, Shouto stretched his arms. Izuku tensed, ready to help however he could when Shouto jumped on the villain. But instead, Shouto started eating the soba. "Mmm, this is good. Just the right amount of seaweed."

"I like extra seaweed too." Dabi smirked, head resting on his hand.

"How have you been doing, big brother?"

"Oh, the usual. Perfecting my goth look, doing some freelancing villain work, and plotting patricide. I have a video of family secrets and a dance routine prepared. I've also been running an Endeavor antifan site under the name BlueFlameRevenge."

"No way!" Shouto yelped, sloshing his bowl in his excitement. He set it down and leaned forward. "I'm such a big fan. In fact, I'm one of your biggest commentors. Do you remember ColdSobaLover?"

"You're ColdSobaLover?!" Dabi screamed loud enough to echo around the metal walls. "Noooooo way! I love your conspiracy theory blog! I check it for updates several times a day. That theory you had about Lady Nagant dating Star and Stripe, it was inspired."

"Thank you." Shouto blushed. "Your comments mean a lot to me. I have barely any views. You're my only follower. I would have stopped posting a long time ago without you liking and commenting on every theory. Dad always acted like my hobby was worthless because it wouldn't help me become number one hero. Also blah blah something about me slandering heroes and embarrassing the HPSC. Throughout middle school, I had to update my blog in secret. You're the person who convinced me to keep on trying when I nearly gave up."

"It's not your fault that some people don't appreciate genius." Dabi grabbed Shouto's shoulders. "Never stop speaking the truth. That blog of yours gave me strength during a rough period in my life when I was struggling to survive on the streets. I'm so proud of you, little brother. Dammit, now I'm not going to be able to kill you to take revenge on our father. I could never be villainous enough to remove such talent from the world. It would be like burning Shakespeare's lost play."

"That's so sweet!" Shouto hugged Dabi. "I love you, big brother."

Izuku observed the brotherly conversation, hoping this was all part of Shouto's clever plan to lure the villain into a false sense of security but increasingly worried Shouto had been telling the truth about his promise not to escape. Oh no, did no one ever tell Shouto that you didn't need to keep promises to people who kidnapped you? Izuku hissed, "Psst! Todoroki! Before you agree to say that your brother is the best, we should leverage this competition for something more valuable than a bowl soba."

Shouto's eyes lit up. "Like two bowls of soba? One for each of us!"

The vault door opened, and Tomura lugged in a huge shopping bag. This was their big chance to escape! If only Shouto would attack while the door was open! But the brothers were still hugging! Izuku swore under his breath as the door closed.

Dabi straightened with a smirk. "Hand Job, guess what? It turns out I was telling the truth about being super close to my little brother. We've been talking constantly for years…which I totally knew all along. I tell him how much I love and adore him every day. My little brother is the cutest in existence." He patted Shouto's head.

"My big brother is cooler than you, Hand Job," Shouto chimed in, then returned to eating his soba.

"Nice try, but I'm about to make my sensei proud and win this contest," Tomura said.

Izuku sighed. "For the last time, All for One isn't my dad. We've barely even interacted. I'm the Ninth in a line of heroes dedicated to killing him, and I'm still not sure he knows my name. Do you really believe a conspiracy theory from this goth wannabe who looks like lead poisoning crept into his brain via his piercings?"

Tomura dumped his bag across the table, nearly knocking over the soba. "Little brother, you can have my entire All Might collection if you say that I'm the superior big brother."

The world seemed to stop. A ruin of All Might merchandise spread out before Izuku: figurines with their heads decayed off. Posters marred by knife marks, paint, and slashes. Clothing with All Might's famous smile burned away. A Mighty backpack, ripped in two. Newspaper articles with swords doodled sticking out of the number one hero. A pitiful stuffed Bear Might toy with its head literally embedded up its ass.

A fist seized Izuku's heart. Even that moment when the doctor had diagnosed him as quirkless could not compare to this horror. He would rather have been burned by Kacchan a million times—he would have preferred his eyes burned out than to see this abomination.

Rocking back and forth in his chair, Izuku mumbled, "That's a Tenth Anniversary All Might poster full of holes! Holes!"

"Oh, yeah, I used it for dart practice." Tomura picked up the poster between two fingers, as if handling a dead rat. "But you can still mostly make out his face. I think that one is in better shape than most of them."

Izuku rocked faster. "Those poor figurines." Tears fell from his eyes. "Oh my god, are those the rare red-blue-and-yellow Mighty sneakers that All Might gifted to last year's professional runners to represent Japan in the Olympics?"

Tomura poked the pile of scraps. "Yeah, I think we stole most of those shoes. Maybe I can put a pair back together for you? There are so many scraps, I think I could piece together one pair. I decayed all the laces, though."

The maniac expression on Izuku's face would have terrified any villain who had ever met the Symbol of Evil. "Only one Diamond Rolex Might watch was ever produced…All Might created it for a charity auction…it vanished before the auction…the long-lost watch is the Holy Grail for All Might collectors! The only unique piece of official merch in existence! Our own version of the One Piece! And you…you…"

Tomura looked at the smashed watch. "In all fairness, my sensei stole that. He wanted to hurt All Might's publicity, and he said robbing the money from charity was a bonus. But yeah, I was the one who smashed the watch. Sorry."

"Sorry?" Izuku threw back his head and laughed maniacally. "Oh, you will be sorry!"

"Are you okay, little brother? Your face is turning purple." Tomura bent over, reaching out a helping hand.

Izuku latched his teeth into Tomura's wrist with all his jaw strength, determined to sever the hand responsible for this war crime against merch collectors everywhere.

"AHHHHHHHHHHH!" Tomura screamed, hopping up and down as he tried to dislodge Izuku.

Dabi laughed. "This is hilarious. You're losing so badly, I almost feel sorry for you. Baby bro, tell me that you love me again."

"I love you, big brother," Shouto said obediently. Then he slurped his soba.

"It's not my fault I got the super feral one!" Tomura wailed. Blood splattered as he hopped around the room. Izuku's teeth reached bone.

Dabi ruffled Shouto's hair. "Shouto, tell me that I'm the best big brother in the universe."

"You're my best big brother after Natsuo," Shouto said.

Dabi's hand stopped moving. "Hey! Why am I second best after Natsuo? I'm the oldest, and that makes me the best!"

Shouto said, "Natsuo never became a villain, never kidnapped me, and never tried to kill me. So he beats you. You can be the third best brother in the universe, after Tensei Iida. Tenya Iida says that his brother is the best in the universe so often that it must be true. He even wrote a book on the subject. I can't argue with five hundred pages on the awesomeness of Tensei Iida."

"Now I'm ranked after someone else's brother who you've never even met?" Dabi wailed, clutching his hair. "This is unacceptable!"

"Help," Tomura whimpered, his eyes crossing as the blood loss set in. He sagged to the floor. Izuku released his grip on Tomura's wrist so he could lunge for the throat.

But before Izuku could complete his totally justified murder, Dabi swooped in and grabbed Tomura. "Hand Job, we need to talk. Ground rules must be established for this contest, including other people's brothers not counting." He dragged Tomura out the door, leaving a trail of blood behind.

Still bound to the chair, Izuku hit the floor. Tears overflowed from his eyes. He'd failed to avenge All Might. That merch…that poor, innocent merch…

Shouto knelt down and cradled Izuku like a baby. Mopping the blood off his friend's mouth, he said, "It's okay. We can bring the All Might merch to Eri, and she'll repair it like new."

Izuku gazed up with teary eyes. "Oh, right! Eri can save the merch! Then the Diamond Rolex Might watch will be all mine." Now that he had a plan, his sanity was restored. He spat out a bloody chunk of skin.

Shouto pulled out a keyring from his pocket and uncuffed Izuku. "I stole the keys when my brother hugged me. After all, he didn't make me promise not to uncuff you."

"You're a true hero." Izuku hugged Shouto. Then he leapt up and pushed the damaged merch back into the shopping bag. He hardly dared look at it as he gathered all of it. But the merch must be rescued. "Okay, now we need a plan to get out of here."

As if on cue, Mirio Togata's blond head poked through the floor. "I found them!" he cried cheerfully, then vanished.

Izuku blinked. "Did you see that too, or am I hallucinating from the stress of so much destroyed All Might merch?"

Seconds later, a boom rocked that vault. The back wall blew up. Natsuo Todoroki's figure stood framed by the billowing ashes. Arms crossed, Natsuo grinned. "I knew it was a good idea to steal those explosives from U.A., along with the boy who can walk through walls. Shouto, I'm here to pick you up."

"Big brother!" Shouto ran forward and hugged Natsuo. "Guess what, Touya is alive."

Natsuo patted his back. "Yeah, I know, he's been stealing the snacks from my room for years. Did he kidnap you? Are you okay? You'd better be okay or I'll kill him." Natsuo lifted Shouto up to examine him for injuries.

Mirio popped up behind them with a big grin. "I'm here too! After all, every underclassman at U.A. is like a younger sibling to me."

The vault door opened. "Did I hear someone trying to steal my little brother?" Tomura stepped into the vault, a bandage around his wrist. "We just agreed not to count outside candidates. Get out, you bug. Izuku, come over here."

Izuku hid behind Mirio. "I pick Togato as my big brother. You're a monster!" His hand clenched on the shopping bag. If he looked at the defiler directly, then his old anger would arise and he would attack. But getting the All Might merch back to U.A. for healing must come first.

Dabi followed after. "Shouto, if you pick me as the best big brother, I'll give you as much soba as you want. I'll let you stay up late and play games. We can work on conspiracy theories together."

"Hmmm." Shouto looked over and took a step forward, toward Dabi.

Natsuo sighed. "Fuyumi is making soba for dinner. Nothing can beat her cooking. After dinner we can make popcorn and marathon the History channel."

"Hmm." Shouto stepped backward.

Dabi held out his arms. "Come with me, and you'll never have to see Endeavor again."

Shouto stepped forward.

Izuku's hand shot out to grab Shouto by the back of his shirt. Between clenched teeth, he said, "Todoroki, I appreciate that you have a complex family situation but right now you are delaying the restoration of my new All Might merch."

As Izuku's eyes flashed green, Tomura made a small frightened sound and leapt backward, knocking Dabi over.

"Sorry," Shouto said meekly, and followed Izuku away as they escaped with the two victorious older brothers.

The ventilator hummed. A single lightbulb dangled over the prisoner tied up in the vault.

Tomura itched at the bandage on his wrist. Addressing the prisoner, he said, "It appears that I still have a lot to learn about being an older brother. My first game ended in a total party kill, so I've decided to research the walkthrough. In non-gamer speak, I kidnapped you to teach me how to become the best big brother."

Dabi crossed his arms. "Yeah, spill your older brother secrets if you're so great."

Cuffed to his wheelchair, Tensei stared with weary eyes. "What unfortunate souls have you two lunatics as older brothers?"

OMAKE TIME!

Omake: All for One's Advice

Tomura: Sensei, why do you have a person-sized bank vault that looks like a bedroom?

All for One: It's for stuffing little brothers into. My own pathetic brother died and turned into a ghost, but I'll need this if one of these days I find a quirk to stuff him into a puppet or a clone body.

Tomura: I bet if I'd locked Hana up in a vault then she never would have died.

All for One: That's the spirit!

#

Omake: Vitriolic Best Buddies

Toga: Boss, why does your sweatshirt say that you only like five people? There are six of us in the League.

Tomura: I don't like Dabi.

#All for One's not on the list either #He didn't even rate a maybe

#

Omake: Dueling Conspiracies

Izuku: How did you convince Tomura that I'm his brother?

Dabi: I pointed out how you stole All Might's quirk. Check and mate.

Izuku: YOU DIDN'T EVEN PICK A HALFWAY PLAUSIBLE REASON! Ahem, not that I acknowledge any plausible connection between me and All for One.

Shouto: You can use the exact same evidence to reach the conclusion that Midoriya is All Might's lovechild.

Dabi: Point taken, but hear me out, he could be the son of both of them.

Shouto: Hmmm…

Izuku: Do not corrupt my sweet, innocent friend with your nonsense!

#

Omake: Lies and Slander

Shouto: Since you're a villain, giving you third best brother is generous.

Dabi: What if I told you that Tomura forced me into villainy?

Tomura: Hey! I didn't even want you in my League!

Shouto: I'm going to need five bowls of soba to believe that whopper.

#

Omake: The Struggle is Real

Izuku: Villain, I only listen to you monologue so that I can tell everything to the police later.

Tomura: You sound like Hana already, Replacement.

Izuku: My father wouldn't appreciate you calling me Replacement Hana.

Tomura: Your first name on your birth certificate was Replacement Yoichi, before your mother got your name changed.

Izuku: I meant my real father, All Might.

Shouto: You've finally broken Midoriya's sanity to the point where he embraced my theory. Shigaraki, for this I raise you to fourth best big brother.

Tomura: Why does someone else's little brother like me more than mine?

#Tomura: Clearly my sensei had a child so I could get a replacement sibling #All for One: Hey, that's my replacement Yoichi, get your own replacement

#

Omake: The Contest Expands

Shouto: If we're going to hold a proper older sibling contest then we need all younger siblings here. Tomura, what about your sister Momo Yaoyorozu? She's clearly actually Hana Shimura. Oh, and Bakugo must be the younger brother of the Second One for All user.

Izuku: Do you have any idea how many generations it's been since the Dawn of the Age of Quirks?

Shouto: Time-travel, silly! Also En is Best Jeanist's older brother.

Dabi: You should read his whole time-travel theory, it's really good.

Shouto: Thank you, big brother. You have risen to a tie with Natsuo.

#

Omake: Bribery

Tomura: Little brother, I've showered you with expensive gifts and you still won't stop biting me. Meanwhile Dabi can get his little brother to call him the winner with just a bowl of soba.

Dabi: And my little brother likes my soba more than all of your expensive crap.

Tomura: Can't you be more easily bribed?

Izuku: I'll say you're the best big brother if you stop trying to kill All Might, quit villainy, and get into therapy.

Tomura: I said easily! None of those things are easy.

Izuku: Also, Todoroki, you should stop being bribed so cheaply. We can leverage this competition for more useful things than a bowl of soba.

Shouto: Like soba for the whole class?

Izuku: You could ask Dabi to stop trying to kill your dad.

Shouto: Why would I possibly want that?

#

Omake: The True Victor

Tensei: I see that you two are in desperate need of guidance. Very, very desperate. From now on, I will shower you with the love and encouragement that you never got from your families.

Dabi: This feels strange. It's like my withered undead heart is growing a size bigger.

Tomura: Can I call you big brother?

Tenya: Hey! These two villains are stealing my big brother! There's only room for one little brother in the Iida family. This means war.

Author's Note: In the end, is this a Dad for One AU? People who know me would reasonably assume yes, but it would also be hilarious if Dabi convinced Tomura to believe a completely incorrect theory. However Inko is a Shimura so Izuku and Tomura are cousins. Or hey, maybe both options are true and Izuku is Tomura's little brother twice over! I'll let the reader decide.