Author's Note: This birthday gift is for Rei, but since she has no canon birthday, I just picked a random day. Really, we can consider Grandfather for One to be a gift to the entire dysfunctional Todoroki family. Thank you to Arceus_Insanity and Giselle_VeraCruz for ideas I incorporated into this AU.

Rei's father loved her hair. Ever since she'd been a small child, he would spend hours combing it. He cut her hair personally, shoulder-length and with the bangs falling over one eye. He preferred to look at her from the left side, where he couldn't see her eye color wasn't green. Father liked to dress Rei up in pretty, fancy dresses. But he also made sure she had sweatpants and sweatshirts to wear. When she wore baggy clothing, she looked just like the sickly green-eyed little boy from her father's childhood photo albums.

The day that Rei ran away from home, she cut her hair short.

Initially Rei slipped into Enji Todoroki's list of arranged marital partners using bribery and a fake ID. After she met him, she revealed that her father was a villain. She needed to marry a powerful hero who could protect her. The Todoroki mansion had an expensive security system to guard against villains who might seek revenge on Endeavor, hopefully able to keep even All for One out. Enji did not take her very seriously when she said her father was the most dangerous criminal in Japan. Since he had never heard of All for One, he assumed the man couldn't be that much of a threat. Still, he promised her protection easily enough. Enji only cared about her powerful ice quirk. After having grown up confined in an isolated mansion for her entire life, Rei had no marketable skills or ability to get a job. But she came from strong quirks on both sides of the family. In fact, her mother had been an egg donor picked for her power. At least Rei could provide Enji with the children he wanted.

Rei did her best to be a good wife and mother. With nowhere else to go, she clung to Enji desperately. With no examples of good parenting in her life, she followed his lead. In the end, she'd failed as a mother. She'd resolved to never be as bad as her father, but she'd been worse than him. Even before she'd burned Shouto, she'd known that, because she'd let her oldest son die. Everything had gone downhill after Touya's death. Her youngest son had started to look like a curse to her. The madness when she'd grabbed the teapot had brought her to even lower depths than she'd believed possible. From the moment she'd looked down at little Shouto screaming and her shaking hand holding the teapot, she'd realized she never should have run away. At least her father, with his demented protectiveness, never would have let this happen.

On Rei's third day in the hospital, her father arrived. She was not surprised to open her eyes and find him sitting in the chair at the foot of her bed, watching her sleep. He used to do that a lot as a child. She supposed he was there to take her away. At one point she would have screamed for the doctors and the heroes, but now she no longer cared. Her previous moral scruples and desire for freedom had faded away.

Smugly, All for One said, "You've made a dreadful mess of your life, Rei."

She nodded. For all that her father was a liar, there was no denying such a painfully obvious truth.

All for One said, "You're a failure as a mother."

"I am." She nodded again.

Her agreement seemed to take him aback. He switched to a soothing tone. "It wasn't your fault. It was because your husband—"

"It was my fault," Rei interrupted. She had no will left to resist her father on any other matter, but in this, she would not be moved. She would not let him take her guilt from her. "Nothing justifies what I did to Shouto. I should have died before I did that. Any halfway decent mother would have killed herself first."

It wasn't as if she hadn't thought about it. She'd been eyeing the kitchen knives, contemplating slitting her own wrists, when Shouto had come in and interrupted her. Afterward, she'd cursed a million times the cruel fate that had turned her violence on her son instead of herself.

"Don't say that," All for One growled, his eyes flashing red. "I won't ever allow it." He took a deep breath, visibly calming himself. He reached out to brush her hair over one eye. "I'm going to look after you from now on."

Rei had prepared herself for this moment. Locking gazes with her father, she neatly bowed her head as low as it would go, touching the bedsheets. "Please protect my children, Dad."

"Of course I will." He lifted up her head. "They're my precious grandchildren."

Quietly and without resistance, Rei followed All for One out of the hospital. No one tried to stop them.

Ever since she'd been little, Fuyumi had always been considered the quiet one. The good girl. The obedient eldest daughter. She threw herself into housework to keep her father happy and pacified. She did her best to sooth Touya's temper and mediate between him and Natsuo. After Shouto was born, when their mother plummeted into depression, Fuyumi took over feeding her baby brother and changing his diapers.

All the adults praised Fuyumi for being a good girl. Her teachers adored her. No one understood the cold burning fury deep inside her heart. It shouldn't be like this. Her siblings should all be safe, happy, and loved. She longed for the strength to protect them. They were her precious jewels. She wanted to take her brothers and put them in a special perfect world where nothing could harm them. But since she was weak, she could do nothing except bow and scrape and appease the adults around her.

On the day the tall man with white hair arrived, Fuyumi knew something was wrong immediately. She'd always had a stronger power than she let on, because she didn't want to make Touya jealous and because her father preferred girls not to be strong. She could sense even small changes in the temperature, enough to know the instant someone new entered the house.

Their father always stayed out late at work. A guest would have rung the doorbell. Fuyumi went to the phone, but the line had been cut. She gathered Natsuo and little Shouto and barricaded them into the dojo. If thieves had come, hopefully they would take the valuables and leave the children alone.

The tall man kicked down the door with one foot.

Immediately, Fuyumi leapt in front of her brothers, teeth bared and icicles forming into razor-sharp nails.

The stranger smiled approvingly. "Ah, I see you're the older sibling." He knelt down, eye level with her. "What a good girl, protecting your little brothers."

Fuyumi hesitated. If the strange adult didn't want a fight, then she saw no sense in starting one. She couldn't win. She lowered her arms and bowed politely. "I'm Fuyumi Todoroki. Who are you and what do you want?"

"Very good." The stranger smiled wider. "You're smart and cautious."

Behind her, Shouto whimpered. Natsuo clamped a hand over the youngest's mouth, eyes on Fuyumi, waiting for her to signal what to do next.

Glancing their way, the stranger said, "Your brothers trust you."

"We only have each other," Fuyumi said. She did not entirely like the possessive way this man eyed them. "Our father would pay a ransom for us."

"Your father is dead." The stranger shrugged carelessly, but the dancing mischief in his eyes left little doubt who had done it. "The biggest piece of him for his casket is a finger."

Running back, Fuyumi clamped her hands over Shouto's ears and glared. It wasn't as if she cared about her father. But her youngest brother shouldn't hear that!

The tall man threw back his head and laughed. "Oh, what lovely hatred in your eyes! You don't feel sad that your father is dead, do you? I understand. My father was a violent man, too." He held out a hand to her. "My name is All for One, but you can call me Grandfather. Come with me, and I will look after you and your siblings. I already have your mother."

Fuyumi eyed him warily, not sure if she believed him. Should she tell her brothers to run for the window while she held the man off? They shuffled nervously behind her.

All for One said, "I have your brother Touya, too. He's in a state between life and death, but he'll survive. I'll make sure of it."

The fight went out of Fuyumi. Her beloved oldest brother, her first treasure? If there was any chance of seeing him again, then she had to take it. Her family had to stay together. She held out her hand. "Promise that you won't separate me from my brothers."

All for One took her hand. "I promise, Fuyumi Shigaraki. Family should stay together. Besides, if I tried to separate you from your brothers then I imagine you'd freeze my heart into an icicle."

In that moment, she felt understood for the first time in her life. It was as if All for One completely saw through her mask as a good girl. She did not yet know if she liked it.

The mansion had rooms for each of the children, full of books and toys. The windows had one-way glass, but there was a giant greenhouse to let in sunlight. Rei came out of her bedroom and hugged her children. She seemed very hesitant to hug Shouto, who still had bandages over his face, but he clung to her.

All for One led Fuyumi downstairs to the basement. Touya floated in a glass tank, a breathing mask attached to his mouth. He had burn scars and stitch marks all over. But the bubbles from his mouth proved that he still breathed.

Gasping, Fuyumi ran over and placed her hands on the glass. "Touya, Touya, Touya," she murmured like a prayer.

Looking down at her, All for One said, "You're protective of him, too, even though he's older." His tone was difficult to read.

Fuyumi put her hands on her hips. "Older or not, Touya has never been sensible! He doesn't know how to look after himself."

All for One laughed and ruffled her hair. "That does seem to be the case. I think it will be you, Fuyumi."

After those cryptic words, he let her read her brother's medical files and even explained he difficult parts. Touya would not wake up right away. But his body was healing. He would live.

Fuyumi wept from joy that night. Her happiness washed away even her concerns about her new living situation. Survival of her family came first.

As the children adjusted to their new home, All for One showered them with gifts and entertainment. He watched old movies with them and cooked. They did not go to school. Fuyumi didn't mind, because school had just been another place where she had to pretend to be good and obey adults.

Shouto warmed to All for One right away. The poor little boy loved living in a house where he didn't need to train for heroism, only play like any other child. He thrived on the positive attention, crawling all over his giant grandfather. In return, All for One doted on Shouto. According to their grandfather, Shouto's every whim was a command. If Shouto wanted a toy he saw on a TV advertisement, it would be delivered within the hour. If Shouto had a food craving, All for One would order a separate dinner just for him. When they played together, All for One handled Shouto very gently as if touching a fragile glass figurine. Shouto was happy to do whatever his grandfather wanted—including dyeing all of his hair white so he fit in with the rest of the family.

Natsuo was warier of All for One at first. After all, Natsuo had also heard the cold decree of their father's death and probably had some suspicions. Although Natsuo had hated Endeavor by the end, that didn't mean he would immediately warm to a dangerous killer. All for One was patient, coaxing Natsuo out of hiding to play with him and Shouto. When All for One offered Natsuo a powerful quirk, Natsuo was finally completely won over.

Rei rarely left her room, only when her father thought she needed fresh air. She did not do much of anything except reading and crossword puzzles. In this household, Rei had no authority. She deferred to her father completely and unconditionally.

Yet strangely, Fuyumi's authority persisted. Her grandfather encouraged her younger siblings to obey her. Although All for One made sure Fuyumi did not need to do chores any longer, he put her in charge of watching over her siblings frequently. He even consulted her on their likes and dislikes, as well as matters like bedtime routines. Fuyumi had to admit she felt a flicker of appreciation for the first adult who seemed to respect her.

After a few months of vacation and play, All for One brought in the shadow-faced Kurogiri to tutor the children. The giant Gigantomachia appeared outside the mansion as a playmate and guard on the occasions when the children were allowed out in the yard.

During schooling, All for One took Fuyumi aside. "As the oldest, you're my successor. I would like to offer you special training."

Fuyumi hesitated. "Touya is oldest."

"Touya seems to be a bit of a mess." With just one sentence, All for One perfectly encompassed Fuyumi's own opinion of her oldest brother. "He's not oldest sibling material. Not after what happened between him and Shouto. Yes, Rei told me. I only blame Endeavor for encouraging rivalry between the boys. If you work with me, Fuyumi, we'll both make sure it never happens again. I promise that I'm working to wake Touya up as quickly as possible. But even after he awakens, he will have a mind younger than his body. I don't believe Touya will be able to lead the family. Certainly not as effectively as you."

Fuyumi felt flattered. She could not deny it. No one had ever called Fuyumi a leader before. She was just the good girl who made sure the chores got done. Her father would have laughed at the notion of making her into his successor, no matter how strong her quirk. Her grandfather had assessed her and found her worthy. It gave her a warm feeling under her chest. Yet she feared how badly this would hurt Touya's pride. "My big brother won't like it. He's always got to be number one."

"I'll teach you how to handle your brother," All for One promised. "Fuyumi, I understand you better than you know. My parents were absent. I raised my little brother all alone, from the time I was your age."

Fuyumi raised her gaze from the floor, surprised. "Oh."

"I see a lot of my dear little brother Yoichi in your brothers. Yoichi was quirkless like Natsuo, shy like Shouto, and had a sickly body like Touya. And I see a lot of myself in you." All for One tilted up Fuyumi's chin. "You're brave, clever, and resourceful. You live to protect your younger siblings. I know because I was the same way."

"You don't think I'm weird?" Fuyumi asked, looking down again.

"You're a special kind of older sibling. That makes you better than everyone else." All for One spoke with assurance. "You and I, we were forged in fire. Because we had to grow up alone without depending on anyone else, we honed ourselves into blades to protect our siblings. I understand you, Fuyumi. If you join my side, then I will make sure nothing can ever hurt your brothers again."

That was all she'd ever wanted. So once again, she accepted his hand.

All for One took Fuyumi aside for personal training in combat and using her quirk. Unlike her father, he never beat her during training and was lavish with his praise. He loaded her down with extra quirks to make her even stronger. It delighted him to learn she had a rare body capable of handling multiple quirks. He said she must have gotten that from him.

Their hours together were long, double what time her siblings spent on tutoring. He also took over her book lessons. Though he pushed her to her limits, she took pride in meeting his expectations. He taught her all about the corruption of hero society. The current society had been twisted since the dawn of the age of quirks, the laws written to control powers by people who hated metahumans. Their family would put it right. He told her about the legacy of thieves who had stolen her great-uncle's quirk. It was only right that she help her grandfather get his little brother back, since he'd helped her keep her own siblings safe.

In addition, he taught her tricks for keeping her little brothers under control. Fuyumi preferred a more delicate hand. Her brothers were plenty obedient, she only needed to nudge them a little to convince them the outside world was dangerous. Besides, Mom wasn't well and needed them close to her side.

With All for One, Fuyumi felt strong. She felt understood. She felt ready to stand by his side. They'd been discussing villain names. She liked Absolute Zero, but on the other hand All Ice had a family theme.

On the day that Touya finally woke up, All for One let Fuyumi alone be in the room with him. He'd used a combination of many quirks to almost completely heal Touya's injuries, leaving only faint scars behind. Privately, All for One whispered to Fuyumi that he'd deliberately deaged Touya a few years in the process, in order to make it easier for her to take control. She adored his consideration. Her grandfather was the best. Privately, she wondered if he might have something to do with Touya's new head of white hair, too.

Mist rose off the capsule as the door opened. Touya half-fell out. Fuyumi immediately caught him and wrapped him up in a blanket. She felt pleased her grandfather had allowed her this honor, respecting her place as eldest sibling.

"You're safe now, Touya," Fuyumi murmured, patting his wet hair. All for One watched them approvingly, letting her handle this. He'd said Touya would trust her more at first.

"Y-yumi?" He cracked an eye open. "I was burning."

"I've got you. You're safe."

Touya whispered, "I have to apologize to everyone."

Fuyumi shook her head. "No, you don't. Dad was wrong to ever try and make you into a hero. You'll see, Touya. I'll explain to you about how hero society is corrupt and rotten. Then we'll rip it down together."

He gazed up at her, wet, shaking, and confused. She guided him to a bed. There would be time later to catch him up on everything that had happened. Time to rebuild Touya's bonds with the rest of the family, especially Shouto. Time to make him understand their family mission.

And if Touya wasn't willing to join her as her righthand man, well…that was what the vault was for.

OMAKE TIME!

Rei: Only the Todoroki family security will keep me safe from my villainous father.

Touya: Mom, our family security sucks. In the universe where I became Dabi, I used to steal food from the kitchen for years. No one ever noticed.

Rei: Then I'm not getting anything from this marriage. Time to bail.

#

Endeavor: Nothing could make my family more dysfunctional.

All for One: Hi!

Endeavor: One thing could make my family more dysfunctional.

All for One: I wasn't the greatest father to Rei, especially the part where I let her escape. But I fulfilled the dream of every father-in-law: kill his son-in-law!

#

All for One: I'll be a good grandpa and love all my replacement Yoichis equally.

Shouto: I want All Might merch.

All for One: What are kids allowed to see on TV these days? There are no family values anymore.

#

Dabi: Awesome, an AU where I'm All for One's grandson. I assume I'll become his successor.

All for One: I'm afraid you're just not insanely overprotective enough.

Dabi: I've got the insane part down.

All for One: You've been disqualified for strangling baby Shouto. That was a disgraceful act as a big brother. Younger siblings can become older siblings in spirit just like how I rewrote history to convince everyone that Yoichi was my younger brother even though his name means First Son. Fuyumi, would you like to become my successor?

Dabi: This is an outrage!

Fuyumi: Can I put my big brother in a vault next time he whines?

All for One: You would be encouraged to do so.

Fuyumi: I accept.

Author's Note: The world should be afraid, I think Fuyumi would be more competent as a villain than the entire League combined.