Author's Note: Today's birthday gift recipient is a surprise. Thank you to joey for this fun prompt, and everyone on Silver's Vault for brainstorming. It's an old enough idea that I hope you don't remember all the twists.

To be honest, Izuku had intended to troll Shouto Todoroki, not All for One. Lately Shouto had been persistent to the point of annoying with his theory that Izuku was All Might's lovechild. Sure, Izuku viewed All Might as a father figure and secretly wished it was true. But in reality, Izuku's biological father had run off shortly after his quirkless diagnosis, and Izuku had gotten tired of being reminded about it. The itch built up for weeks, finally culminating during a villain attack.

All for One had attacked U.A. during an outdoor training exercise. The villain had come for Izuku with a vengeance, knocking most of the students and Aizawa against the school wall. The Dekusquad surrounded Izuku protectively. It was no time for jokes.

Yet with a completely straight face, Shouto said, "See? All for One is targeting you because you're his mortal enemy's son." Then he knocked off All for One's helmet with an icicle, revealing his scarred face.

Izuku couldn't resist a perfect cue like that. He gasped, pointed at All for One, and cried, "Dad?!"

A stunned silence fell across the damaged field. The first person to speak was Katsuki Bakugo, who got up from the wall and growled. "That's not your dad, you moron—"

Denki elbowed Katsuki into silence. "Shut up, this is hilarious."

Tears streaming down his face (he'd always found it easy to cry on command), Izuku wailed, "Dad, how could you lie to us and say you were working abroad in America?"

All for One actually took a step backward. "I didn't…I'm not…There's been a mistake…" The garrulous villain was at once at loss for words.

Izuku hadn't expected his trolling to have such an impact on the supervillain. At least it was working as a tactic to stall for time while the adult heroes arrived. He doubled-down on his lie. "I'd know your obnoxious lecturing voice anywhere. I would have realized right away if the helmet hadn't muffled you."

Ochaco gasped exaggeratedly. "You two even look alike." Izuku was fairly certain she knew about his lie and was only playing along. He didn't look like a potato!

Tenya muttered, "The villain was targeting Midoriya this entire time. Very suspicious." Izuku was less certain if Tenya believed it or not. He'd have to be extremely clear with his friend later that the villain had been targeting him for his quirk.

All for One peered down. "Ninth, you have the exact same eyes as my little brother. Almost as if you're a descendant of his…But that's impossible. Yoichi was so gay, he scored seven out of six on the Kinsey scale."

The villain's voice started to become more confident. It didn't seem like the ruse would last much longer. Izuku raised his fists and braced himself for the fight to resume.

Then Denki Kaminari jumped up and waved his hand. "All for One is also my long-lost father!"

All for One whirled around. "Who on earth are you?"

Shamelessly, Denki said, "I see you've finally returned, Dad. Did you ever pick up the milk?"

With fake surprise, Tsuyu Asui said, "My father also ran away saying he had to fetch a carton of milk. He used the same lame excuse on you, brother?"

"Sister!" Denki cried, grabbing her in an exaggeratedly tearful hug.

Hanta Sero pounced on the group hug. "I'm All for One's son too."

Trembling, Rikido Sato squeaked, "Me, too."

Kyouka Jirou shrugged. "Sure, I'm All for One's daughter. Why not? The publicity will be great for my music career."

Mezo Shoji said, "I've been hiding my face because of our resemblance, Dad."

"You can't see me, maybe we look alike," Toru Hagakure suggested impishly.

Softly, Koji Koda said, "I'm bald, All for One could be my father."

Eijiro Kirishima puffed out his chest. "I'll bear this burden for the class like a man. The true son of All for One is me!"

All for One's eyes darted between the students. Izuku couldn't believe this seemed to be working—as a distraction, at least. Yuga Aoyama had curled up in a ball and muttered in French. Momo looked between her classmates as if they had all gone insane. Mineta had run away some time ago.

Fumikage Tokoyami spread his arms wide, Dark Shadow wrapping around him like a menacing cape. "May the spirits of darkness curse you for never paying child support, Dad."

"Bird boy is definitely not my son," All for One said in a confused way.

Mina Ashido laughed wildly. "This document of unpaid child support says otherwise." She pulled up a form letter she'd found on her phone. With her hasty typing, the document claimed that All for One owed child support for everyone in Class 1-A.

Shaking with joy, Shouto cried, "This is the greatest day of my life. So many secret children! I wish I could also be All for One's son because anyone would be better than Endeavor. Can I be? Will you adopt me? You've got so many kids already."

Eri banged on the window and shouted, "Daddy!"

All for One's gaze snapped to her. "Oh, dear, you do have white hair and red eyes. And you would have been born after I divorced my wife. You're a real risk."

Vlad King stormed out the door, leading Class 1-B to join the defense. Immediately, Aizawa leapt up and grabbed Vlad by his shoulders. "Hey, All for One, here's your secret son. He even dresses like you."

"What are you doing?" Vlad growled, trying to jerk away. "Eraserhead, my father lives in a nursing home, you've met him."

"All for One looks like he belongs in a nursing home," Aizawa said stubbornly. "That's proof."

"Aren't you going to claim to be All for One's son like the rest of your class?" Vlad demanded.

Aizawa stared. "No, I'd rather inflict him on you."

"Class 1-B will not be outdone!" Neito Monoma declared grandly. "The true son of All for One is me! It's only natural, look at my quirk. Give me a few minutes and I will have testimony from my parents to prove it. They love a good prank."

Every student in Class 1-B started shouting about All for One being their father. Manga claimed that facelessness was hereditary. Ibara said she couldn't lie but also strongly implied she wanted a DNA test.

All for One's jaw hung open. "Just how many are you?"

A throat loudly cleared. Mashirao Ojiro leaned against the wall with his arms crossed. The usually calm student glared at All for One with the burning force of a thousand suns. His tail lashed angrily. Slowly and deliberately, he growled, "Cheating on Mom? Now I know the real reason for your divorce. How dishonorable, Dad!"

"Son—I didn't—I swear I didn't!" All for One took a step backward. Ojiro advanced. With a frantic squawk, All for One insisted, "I can prove my innocence. I'll be back with DNA tests." Then the villain fled.

Together, the students cheered for their victory in sending a deadly enemy sent running.

Class 1-A had gathered in their classroom, eating mochi to celebrate. Clapping Izuku on the back, Kirishima said, "That was an inspired idea."

"It was stupid and should never have worked," Katsuki groaned.

Shouto beamed. "It doesn't matter if All for One has a real child or not, this is the happiest day of my life."

"Don't forget about our MVP." Toru slapped Ojiro on the back. "I never knew you were such a convincing actor."

"That's because I wasn't acting," Ojiro said. "Well, I faked my outrage because I knew you were all lying. Except I wasn't. I've been wanting to tell everyone for a long time, but I didn't know how to put it into words." He took a deep breath. "All for One is my father. He and my mother got divorced after she found out about the villainy. I used to live with him on weekends, before I started hero school. He was a surprisingly decent dad. Still, I decided to become a hero because I wanted to be different from my father and oppose his villainy. Anyway, I'm pretty sure that All for One ran off because he thought I actually believed all of you. He was mortified that I might think him a cheater and wanted to prove his innocence. He's been texting me with illicit DNA tests ever since."

Silence filled the classroom for a bit too long. Then everyone exploded into laughter.

"Good one," Denki said, wiping a tear of mirth from his eye.

Hanta snorted. "Yeah, you said it with such a straight face that I almost believed you for half a second."

"I didn't," Katsuki insisted. "Tail, a villain's son? Get your normal-looking boring face out of here. You might as well claim to be Godzilla's lovechild."

"It was a good joke." Kirishima smiled.

"I never knew you had such a crazy sense of humor, Ojiro." Kyouka giggled.

Ojiro looked between his classmates. "I'm serious. I hope you'll all still treat me the same way."

Everyone laughed even harder. Shouto said, "Nice try, but even I wouldn't believe such a whopper!"

Sinking down in his seat, Ojiro sighed. Why would no one take him seriously, even though every word he'd said had been true? Did he just seem too normal to be a villain's son? It wasn't all bad. He felt relieved he wouldn't have to deal with his friends treating him differently or possible ramifications from his school. Now that everyone had gotten so determined not to believe him, All for One wouldn't be able to use this information to blackmail him. Yet Ojiro couldn't help being a little salty. Did he truly seem too boring to have an exciting secret backstory?

Sometimes being too normal could be both a blessing and a curse.

OMAKE TIME!

Omake: The League Reacts

Tomura: Sensei fathered all of Class 1-A? I don't know if I should be more concerned that I nearly killed my younger siblings or upset that he's a deadbeat dad.

Dabi: Being a bad father is definitely the worst crime.

Tomura: Toga, the squirts with green hair and round cheeks are now off-limits for stabbing.

Toga: Awwww! Why can't I? They're related to you, not me.

Tomura: I have such a bad track record with killing family. This could be difficult. I'm scared to fight them now.

Twice: We'll help you! (No, we won't.)

Tomura: I'm going to need so many bank vaults.

Spinner: Bank vaults?

Tomura: Where you stick younger siblings, obviously.

Spinner: Can I have a vault to play video games?

Tomura: I'm going to need dozens. Why not?

#

Omake: Family Preferences

Denki: My mother had spiky hair.

All for One: Uh-oh, I might need a DNA test.

#

Omake: Aoyama's Internal Monologue

Aoyama: Oh no, what do I do? I can't pretend to be All for One's son. He's met my parents. He'd never believe it. But it will look suspicious to the rest of the class if I don't say anything. I'll just rant in French. That tactic never fails!

#

Omake: From the Void

Yoichi: Big brother, did you ever get a DNA test on your son?

Ojiro: Hey! What did I do to deserve that?

Yoichi: I'm sorry, your hair is just so normal.

Ojiro: You're dead to me. Deader.

Yoichi: I didn't mean to hurt you, I'm trying to help you. No one would want to be All for One's relative if there was even the tiniest chance of escaping that cruel fate.

Ojiro: I bet you like Midoriya better.

Yoichi: Please come back, I'm sorry!

#

Omake: All for One's Poor Education

Tomura: If the hero brats aren't actually yours, then why did you run away?

All for One: Social services scares me more than the incompetent heroes. It's difficult to be sure, sometimes babies spontaneously spawn in rivers near their parents.

Tomura: I have no formal schooling, and even I know that's bogus.

All for One: Also, I have trouble keeping track of all the couples I persuaded to have children as part of a Machiavellian scheme. That's how I adopted you.

Tomura: I thought you found me on the street.

All for One: See, children do sometimes spawn randomly.

#

Omake: Darth Vader Fail

All for One: I'm here to reveal that Mashirao Ojiro is my son! Muhahahaha! Now, my son, watch as all the hypocritical heroes turn on you.

Izuku: You're just copying my prank. Who's your next fake lovechild?

Shouto: I volunteer!

#

Omake: The Birthday Club

Izuku: We've gathered here from around the multiverse to discuss the trials and tribulations of being All for One's son.

Ojiro: Actually, I had a perfectly happy childhood. My parents never fought in front of me even after the divorce. My father always kept his villainy away from me. He was a good dad. We did father-son bonding activities on the weekend.

Izuku: You never got vaulted?

Ojiro: What does vaulting mean?

Izuku: Even as the son of All for One, somehow you're still normal!