Hisashi Midoriya took his coat from the closet, folded it up, and placed it in his suitcase. He was careful not to wrinkle his bespoke suits wrapped in tissue paper. Moonlight shone through the small window on the front door. Among many other quirks, Hisashi had the power to see in the dark. He'd left the light off so as not to disturb his sleeping family.
From the stairway, Izuku called, "You're home, Dad!" The six-year-old boy ran forward and tackled his father's waist.
Hisashi spun around and caught his son up in a hug. He nudged his suitcase out of the way with his foot. "Just briefly, ducky. I'm leaving on a business trip." Hisashi had an important meeting with a major yakuza group in Hokkaido, under his villain identity All for One. He'd only dropped by his civilian house in order to pick up his heaviest winter coat. "I didn't mean to wake you up."
Izuku drew back. He gnawed on his lower lip. "I thought you came home for Mom's birthday."
"Oh, was that this week—?" Hisashi winced as he calculated the days in his head. His wife's birthday was two days away. "I won't be able to make it this year. My work project is very important. I'll mail her lots of gifts as an apology."
Izuku's eyes welled up with tears. He sniffled. "Please, Dad? Mom will be so disappointed. Especially after you missed her last birthday."
Had he? As an ancient villain, Hisashi found it difficult to keep track of events as frequent as once a year. His own birthday meant nothing to him, so he didn't understand the fuss. But Hisashi hated to see his son cry. "Don't be sad, ducky. I'll buy you a new tricycle. How about that?"
Izuku stomped his foot down. "I don't want another toy. I want us all to celebrate Mom's birthday as a family." Waterfall tears streamed down Izuku's cheeks as he wailed.
"Shhhhh, shhhhh." Hisashi glanced at the stairs, afraid his wife would wake up. Desperate times called for desperate measures. "I'll get you a new All Might figurine if you stop crying."
Izuku glared through his tears. "You should be making it up to Mommy!"
"Yes, yes, she'll get extra presents too." Hisashi felt certain his wife would understand that work came first since he was the breadwinner of the family. Not that their family was in any danger of running out of money, but he could always lie about that.
"Will you help me prepare my birthday present for Mom?"
Anything to stop his son's tears from flooding the hallway, including Hisashi's dry clean only suits. "Yes, of course." Hisashi glanced at his watch. He could spare an hour or two.
"Follow me." Izuku marched down the hallway with his head raised high. Next to the pantry, Izuku tapped on a blank part of the wall. A hidden door popped open. It swung backward, only darkness visible within.
Hisashi gasped. "Ducky, how did you find out about that?"
Izuku said, "It's my secret hideout." He ran down the stairs too fast for his father to stop him.
Heart racing, Hisashi chased after. When he'd first built this house, he'd prepared a secret basement with a habitable bank vault…just in case. Surely Izuku couldn't realize the meaning of what he'd found? If Izuku had told his mother, then this vault might need to be used early.
The finished basement had maroon carpet, a cabinet full of weapons, and a kitchenette for feeding prisoners. To Hisashi's horror, the vault door hung open, revealing metal walls covered in padding, a ventilator, a composting toilet, and bed. Izuku walked right past the vault as if he didn't notice it. Hopefully a six-year-old was too young to realize how sketchy this place looked. Right? Hisashi was prepared to break out the expensive overseas All Might merchandise in order to keep Izuku quiet.
Standing on his tip-toes, Izuku took down a box from the shelf. "I got Mommy a bracelet for her birthday. I need someone to try it on to make sure it fits."
This sounded like an unnecessary task, and their wrists weren't the same size, but Hisashi just wanted to be out of here as soon as possible so he could start damage control. "Sure." He held out his arm, keeping his eyes on the stairway. The secret door hung wide open. If Inko woke up, she would see it.
Metal fastened around Hisashi's wrist with a clack. Then Izuku slammed his full weight into the backs of his father's knees, shoving him into the bank vault.
In his surprise, Hisashi fell to his hands and knees. The vault door locked behind him.
Hisashi sprang to his feet, ready to use his many quirks to rip and rend the metal open. But nothing happened. Hisashi gaped at his outstretched hand without a hole on the palm. "Huh?" The metal cuff on his wrist crackled and glowed.
From behind the door, Izuku called, "I got a prototype quirk suppressant made in David Shield's laboratory by winning an All Might trivia contest. No one else guessed All Might's top speed."
Curse All Might, giving away such dangerous tools to children! Hisashi winced when he remembered he'd given his son that information about All Might during a session bragging about how Daddy was even faster.
Striving to sound like a calm and reasonable adult, Hisashi said, "Izuku Midoriya, you need to let me out right this instant."
"Nuh-uh. Now you can't leave on business." Izuku giggled. "You're staying in there until Mom's birthday. You're my present for her! Don't be sad, Daddy. I filled the secret room with all sorts of stuff that the internet said dads like: majong, sake, and baseball!"
Hisashi gasped. "You vaulted me? Oh, ducky, I'm so proud of you!"
"You're not mad?" Izuku asked hesitantly.
"How could I be angry when you just showed how much you love and appreciate me?" For the first time, Hisashi finally had a family member who loved him in return as much as he loved them. He'd never felt so much pride and joy in his heart. Though not a crier, a tear rolled down Hisashi's cheek. "You took after my side of the family! Except me specifically, not my foolish little brother. This is the happiest day of my life!"
"Okay, but I still won't let you out." Izuku sounded suspicious. "I have to go to bed before Mommy notices. Goodnight!" With a pattering of feet, Izuku ran up the stairs. At least it sounded like he'd closed the secret door behind him.
Hisashi looked around. The room looked the same as he'd left it, except for the addition of a mahjong board, a crate of sake, and a television hanging in the right corner. What was Hisashi supposed to do with a mahjong board and no one to play with? He'd never been a drinker. And the television didn't have a remote control. That was six-year-old logic for you.
Despite Hisashi's pride in his son, he still needed to attend his business meeting. He went to the wall and opened a panel by the door. Hisashi had installed a safeguard in case his hypothetical prisoner was in distress. The red button would summon Kurogiri. A prisoner wouldn't be able to escape, because Kurogiri wouldn't obey them, but Kurogiri would apply medical attention as needed. Of course Kurogiri would immediately let his master out.
Hisashi pressed the red button. The television overhead flared to life, an announcer crying, "Curveball below the knees! And he's off and running!"
What in the name of villainy? It took a moment for Hisashi's brain to catch up to his eyes. A baseball game played on the television. Hisashi pressed the button again. The volume got louder.
Somehow, probably without knowing what he was doing, Izuku had disabled the alarm to hook in his new television instead. For the first time, Hisashi started to worry.
Hisashi's father had loved baseball, the biggest reason why Hisashi himself hated it. When the tedious game was over, it started playing again. The recording was on loop. Hisashi screamed and smashed the button, but that only made the volume even louder. He couldn't escape by covering his ears. The baseball was everywhere, drilling into his brain. Hisashi hopped up and down, trying to smash the TV, but even he wasn't tall enough.
His head ached. His sanity slipped. The baseball continued.
After the fifth repetition of the same baseball game, Hisashi had an epiphany. Could it be that locking people in bank vaults was a form of torture, not an expression of love? Was this how Yoichi had felt?
Nah. Those two circumstances had been completely different. Hisashi would have let his little brother out any time if only the stubborn fool had agreed to join him. Also, Hisashi had kindly locked Yoichi up in a dark, silent vault instead of one playing baseball on repeat. Truly, Hisashi was the best brother ever.
Hisashi curled up on the too-short bed and put a pillow over his head, trying to drown out the endless chanting from the crowd and the sound of a bat striking a baseball. The bed had an All Might blanket, but he clung to it like a child. He could feel his brain cells dying. After Hisashi got out of here, he was hunting down the annoyingly peppy announcer and murdering him.
By the tenth repetition, Hisashi would have bashed his head against the wall and escaped into the bliss of unconsciousness, except he'd padded the vault walls. What a foolish mistake! Hisashi had added that innovation because Yoichi had been prone to self-harm in addition to his other foolishness. But he surely wouldn't have needed that with his Izuku, a sweet and obedient child. (A voice in the back of his head whispered that Izuku had locked him inside a bank vault, but Hisashi ignored that.)
Loud cheers came from the screen. Hisashi gritted his teeth and endured. When the extensive post-game commentary started, he muttered off the list of his quirks to distract himself. When the game played again for the eleventh time, he started sucking on the All Might blanket.
When the vault door opened, Hisashi didn't think. He ran for it.
Electricity arced from the doorway, striking Hisashi and sending him falling to the floor. He groaned and blinked up at the ceiling.
Izuku wagged his finger. "Bad Dad!"
Hisashi slowly stood up, shaking off the tingles. If he'd been thinking, he would have remembered that he'd installed that feature to prevent a repeat of the vigilante brother thieves. He groaned, his numb tongue struggling to find words.
Izuku pushed forward a plate of wasabi. Nothing except spicy green paste filled the bowl. "The internet said that dads love wasabi. Since you've been a mostly good prisoner, this is a treat."
Hisashi's eye twitched. "The baseball…make the baseball stop…"
Izuku pulled out a remote control and pressed the power button. Finally, blessed silence filled the vault. Hisashi whimpered.
Izuku beamed. "I brought you a suit to wear." He pulled over his father's suitcase. "You need to look nice when Mommy comes down to see you for her surprise birthday party."
Hisashi paled with horror. If Inko found a prison cell in a secret basement in her house, she would immediately realize that only her husband could have installed it without her knowledge. She would probably assume he was a serial killer. (He preferred the term mass murderer.) She would freak out. Worse, Hisashi would be locked inside a bank vault while his wife freaked out, and thus unable to prevent her from calling the police.
Between clenched teeth, Hisashi said, "I promise that I'll come to your mother's birthday, ducky. Please let me out."
Izuku crossed his arms. "You promised to come to my last school sports festival, but you didn't."
Hisashi tried to smile, but it probably looked like the Joker's grin. "What. Do. You. Want?"
Izuku pulled out a paper from his pocket. "I have a list! I want you to show up for all family birthday parties. I want you to spend at least three weekends a month at home. I want you to attend my sports festival and compete against Kacchan with me at the Father-Son Cavalry Battle."
"What the f—fidgewidgets is a Kacchan?"
"The previous champion, but not for much longer." Izuku beamed. "With the tallest dad, I'll be unstoppable!"
"If you want to win so badly, then I'll break this brat's legs and his father's, too."
"Nuh-uh. You have to play fair. I have more demands." Izuku ran his finger down his list. "I want you to make pancakes for breakfast on Sundays. I want you to get me a limited edition All Might in Space backpack, a Tenth Anniversary All Might poster, and tickets to the All Might meet and greet event."
Hisashi's smile widened until his mouth hurt. "Fine. You can have all the idiot's merchandise. I'll build a new merchandise factory just for you."
"I want you to teach me to throw a baseball."
Hisashi choked. "Absolutely not! I'm never looking at another baseball for the rest of my life!"
"But Daaaaaaaaaaaad!" Izuku looked ready to cry again. "That's what fathers and sons do! The internet wouldn't lie to me!"
Hisashi resolved to bring down the entire internet across Japan in revenge for this. "One game," he ground out. He could always fake a work emergency and flee the country. Once he was out of here, he could do whatever he wanted.
Izuku pressed the button on the side of the wall. The field of electricity died down. As Hisashi stepped out into freedom, Izuku said, "If you don't keep all of your promises, then I'll tell Mommy about your creepy room in the basement."
…Dammit.
OMAKE TIME!
Omake: Let Him Have His Delusions
All for One: Finally, someone loves me enough to vault me! I'm so happy!
Izuku: I'm doing this for Mom's sake.
All for One: Aw, you're a tsundere. Just like my little brother! Yoichi never would admit how much he loved, admired, and worshipped me.
#
Omake: Breaking News—Hundreds Injured in Local Elementary School Sports Festival
Izuku: I'm so excited for our Father-Son Cavalry Battle.
All for One: (Yawns) Let's get this over with. Wait, who's the brat with spikey hair and why does he have such rancid vibes?
Izuku: That's Kacchan. Dad, why are you making a funny face?
All for One: Entering…PTSD…flashback…about…the Second. Muhahahaha! Ducky, time for us to crush an elementary schooler to work out my unrelated issues!
Izuku: Yay!
Author's Note: The future of this AU mostly went like canon, except All for One spent more time with his family and Katsuki developed a healthy respect (fear) for Izuku. Years later, when Izuku saw the flashback to Yoichi's past in his dreams, he started sweating. Summoning all his powers of denial, Izuku convinced himself that there could be more than one asshole in Japan who liked locking people up in bank vaults.
This fic was written for Cyberphobia's All for One Bullying Week. It's also a birthday gift for my sister, who gave me this prompt. Really, All for One Bullying Week is a gift for all of us, since don't we all want to see All for One suffer for a change of pace?