Chapter Six: Saving the World Without Your Father's Permission is Grounds for a Vaulting

Hisashi advanced, a murderous look on his face. The cat ran between his legs into the room, but he didn't seem to notice or care. Red tendrils extended from his body, blocking off the door. His eyes burned.

"If you've harmed my precious Izuku, I'll see you die slowly. Perhaps you imagine there's nothing worse I can do than kill you. But for each second you keep him from me, I'll visit hours of agony upon you." His eyes fell on Izuku. "You're a fake too, aren't you? I should have known. I had an odd feeling about my so-called brother from the beginning." He laughed bitterly. "Perhaps I wanted to believe too badly."

Yuuto and Izuku exchanged glances. Izuku asked, "Do you think we should tell him?"

"I have mixed feelings." Yuuto shrugged. "I've died once, and I can honestly say I prefer it to the vault. But protecting you is even more important to me, so I'm inclined to tell him."

"Yuuto?" Hisashi shrieked. "That you in there, isn't it, you white-haired terror?"

So much for having a choice. Izuku sighed, the movement hurting his sore throat. Another pitiful cough emerged. He supposed it was for the best at this point. At least the world had already been saved.

Neither confirming nor denying it, Yuuto backed away.

Hisashi growled, "You're the worst brother ever! You stole my son's body!"

"I didn't do it on purpose!" Yuuto cried. "From my perspective, he stole my body!"

Leaping to his uncle's defense, Izuku said, "I was even the one using the quirk when it switched our bodies."

Hisashi looked between them. His gaze settled on Izuku, reeking with suspicion. "You're not four years old."

"My mental age is twenty. We traveled back in time to save the world," Izuku said. As long as he kept the details of Quirk Singularity secret, he could reveal that much.

"Save the world?" Hisashi's nose wrinkled. "That sounds suspiciously heroic."

"Ha! Your son become a hero! He even inherited One for All! Suck it, big brother!" Yuuto crowed. "Sorry, I couldn't resist—I've been holding that in for a long time now."

Izuku said, "Dr. Garaki caused the destruction of the world. Even you wouldn't have wanted it—Mom was dead and Japan was in ruins. We had to kill him."

Hisashi looked at the corpse. "Are you sure? He's more the sniveling worm type than the conqueror type."

Enunciating each word, Izuku said, "I watched everyone I loved die because of him."

Hisashi recoiled. "I'm dead in the future?"

"Ha-ha, no. You clung to life like a cockroach." Izuku snorted.

The stunned and hurt look on Hisashi's face actually made Izuku feel a little bad. Even knowing about the whole villainy thing.

"Sick burn," Yuuto whispered.

Izuku sighed. "You weren't the world's greatest dad in the future."

"I-I wasn't?" Hisashi looked even more upset than when he thought he'd been dead.

"We didn't even have a relationship at all."

The life left Hisashi's eyes. He sagged.

Izuku said, "But if you'll quit being a villain and pay for your crimes, maybe we can rebuild our relationship in this timeline."

"That deal seems rather too slanted in your favor, my sweet little pumpkin." Hisashi straightened, a glint in his eye. "We can see about rebuilding our relationship after you're in your correct body."

"Probably from inside a bank vault…" Yuuto muttered.

"Shut up, body thief," Hisashi said. "I bet you're the one responsible for my estrangement with precious baby in the future."

"Why do you always blame me for everything?" Yuuto threw up his hands in the air. "You know full well I was mostly dead! At best, I could say a few sentences to him in visions! It's not my fault you put your villainous ambitions over your family, as usual."

"He's right," Izuku said. "I think you left us because your business had gotten too dangerous, but you could have chosen to step away from villainy instead. Mom died because you let Dr. Garaki and the monster you created from Tenko Shimura get out of control. This is on you."

Hisashi sighed. "I see my future self neglected to take good enough care of you. I apologize, and I promise I'll do better this time. I'll give you my full, undivided attention."

Izuku had a bad feeling. "What does that—?"

He didn't have time to finish. His father moved behind him in a flash. Tendrils wrapped around him, too fast for him to fight, not that his weak body could put up much of a struggle. A blow struck the back of his neck and the world went dark.

Izuku woke up strapped to one of the experimental slabs.

Needless to say, this was not a pleasant feeling. He instinctively started struggling, but a series of straps from his legs to his neck kept him bound so tightly he could barely twitch. The helmet on his head had wires running to the machine beside him.

He could lift his neck just enough to see Uncle Yuuto strapped to the table next to him. The buckles over a child's body made him look like a mummy. Bright green eyes glared from under the too-large helmet. In front of them, Hisashi fiddled with a computer switchboard. He sported three bandages on his arms and one on his face.

"Whoa, what happened to you?" Izuku asked without thinking.

Hisashi inclined his head at Yuuto. "He bites."

Yuuto struggled even harder against the bonds. "I'll do worse as soon as I get out of these!" He started to gnaw on the leather strap closest to his face with optimistic enthusiasm.

"Stop fussing. I'm just going to switch your bodies back." Hisashi flipped a switch as Inko's cat wound around his ankles. The board lit up.

"Wait, that's actually good," Izuku said. He cast a glance at his uncle. "Unless you don't want to swap back?"

"Of course I want to swap back. I feel like you're getting the worse deal, since you'd be stuck in this weak child's body."

"But my body will grow up someday, while yours will always be ill. Dad said even quirks can't cure you. I feel very bad."

"Do you think I'd want to stick my cute nephew with my health problems? Besides, my body may be a worthless piece of junk but I still feel more comfortable in it than I do as someone else."

"Then we're agreed on swapping back." Izuku half-nodded, straining the strap on his neck. "Should we let him do it?"

Yuuto started struggling again. "Not by him! I doubt he's knows what he's doing!"

Without turning around, Hisashi sighed. "Do you see the kind of defiance I have to put up with, Izuku? He's picking a fight out of sheer spite. I've experimenting with body swapping before, so I know this equipment works."

"Have you ever used it by yourself without your mad doctor?" Yuuto demanded. "Our condition was caused by time-travel, do you know how that might affect the outcome? I bet you don't! You're just absurdly overconfident!"

Izuku remembered the time the world had ended due to his father's experiments. "Wait, Uncle Yuuto may have a point. Can I take a look at the mechanisms behind this technology before you use it on me?"

"I know what I'm doing, baby." Hisashi glanced at a book in his hand, then flipped another switch. "It's very unnerving looking at you two like this, and I want to fix it immediately."

Izuku's bad feeling intensified. "I don't think that's a good reason to rush such an important process."

His father looked at his book, mumbled, then changed the position on the switch back. This failed to inspire any confidence.

"Stop!" Izuku rocked back and forth, trying to dislodge the helmet. "Let's talk about this!"

"Get this off me!" Yuuto chewed at the leather like a woodchuck.

Hisashi sighed. "Why must you two always fight me?"

Yuuto muttered, "If everyone in your family hates you, did you ever think maybe you're the common denominator?"

"Izuku doesn't hate me. Right, baby?"

With both his father and his uncle staring at him, Izuku felt uncomfortable. He mumbled, "Let's just say I don't only hate you."

"Still better than your uncle, so I'll take it."

Yuuto scowled. "What are you talking about? That's exactly how I feel about you, too."

Hisashi blinked. "You don't only feel hatred toward me?"

"Of course I've always struggled with my mixed feelings where you're concerned."

"But you started an entire lineage of heroes dedicated to killing me!"

Yuuto rolled his eyes. "Don't be melodramatic. All I did was accidentally pass along my quirk while banging my boyfriend. It's not my fault you made every single future user want to kill you. You have a natural talent for pissing people off."

Hisashi recoiled. "Don't talk about your sex life in front of me!"

"Oh, please, it's not like I gave you details—all I did was admit I had one."

"Yes, with the person I hate the most!"

"I fail to see what Kaji did to make you hate him any more than the other One for All users."

"He seduced my baby brother!"

"That feels like circular logic. If you hate every person I date, then I can't possibly date anyone you don't hate—"

Izuku interrupted the brotherly argument to shout, "Hey, look behind you!" The cat had climbed onto the computer switchboard and started walking all over it. Switches flipped like crazy. Lights glowed on the machine.

Too engrossed in the argument to hear his son, Hisashi cried, "You were sleeping with someone who wanted to kill your only darling older brother!"

"Because you tried to kill him first."

"How else was I supposed to react to him dating you?"

"Again, your logic is circular. I think you were just jealous I was getting laid and you weren't."

"I was trying to protect you from that punk! He was a bad influence, encouraging your stupid and dangerous ideals."

"Don't kid yourself. I wanted to be a hero far more than Kaji ever did—"

More frantically, Izuku shouted, "Cat! Behind you!" He struggled with all his might, both to attract attention and in an attempt to get free of the helmet. The machine had started to hum. Light sparked down the tubes.

Finally, Hisashi turned around.

The cat jumped on his face, knocking him into the mess of wires attached to Izuku and Yuuto's helmets.

Heat shot through the helmet and lanced into Izuku's head. He screamed as the world dissolved into a kaleidoscope of colors.

When Izuku opened his eyes, he stared at the same grey ceiling. He was still strapped to a table. But if nothing had happened to make his situation any worse after the cat disaster, he would count himself lucky. He blinked away the spots before his eyes.

A curl of green hair fell over his eyes. Green hair? He twitched his fingers. They felt small as a toddler's. "Hey! It worked!" It was a relief to feel One for All's familiar power pulsing through his veins. He'd missed his quirk. "I'm back in my body!"

"Me too!" Uncle Yuuto called from the adjacent slab. He very slightly waved his fingers despite the strap around his wrist. A cheerful grin spread across his usual face. "So my big brother didn't screw up? I'm glad to be wrong for once."

"Meow," someone said.

It was a very strange sound—exactly like a human voice speaking a cat noise.

Both Izuku and Yuuto turned their heads to see Hisashi perched on all fours on a table, licking his own wrist.

"I think you spoke too soon, Uncle Yuuto," Izuku said.

A black cat crawled out from under the fallen switchboard. "What happened?" the cat asked in Hisashi's voice. "Why do I feel a hairball in my throat?"

"Hahahaha! This is the best thing that's happened to me in centuries!" Yuuto laughed so hard tears streamed down his face.

"Dad, it looks like you got caught up in the transfer," Izuku said. "I tried to warn you."

"What are you talking about?" Hisashi asked. "I'm not—" He looked down at his paws. "Sweet villainy!"

Yuuto laughed even harder.

"It's okay. I can fix this," Hisashi mumbled. "I just have to swap us back—" He looked up at the smoking machine. "Please tell me that's not broken."

"It looks very broken to me." Yuuto sounded like he was reporting that Christmas had come early.

Twisting in a way that seemed impossible for a human, the cat started licking himself even lower.

The real Hisashi scratched his human body. "Stop doing that! You're embarrassing me."

The cat-in-a-human's body looked up, hissed, then ran out of the room on all fours.

"Get back here with my body!" Hisashi screamed, chasing after.

After a long moment, Izuku asked, "Did he leave us here tied up?"

"Yup," Yuuto said. He went back to biting the closest strap.

Eventually, Inko came by to rescue them. She carried Hisashi in cat form in her arms.

"I have some bad news," she said as she untied Izuku. "Your father's body ran out of the building and got captured by All Might. He's being carted off to Tartarus as we speak. All Might traced him back here, so we should probably get out of this building. Fortunately, your father and I have numerous secret bank accounts. We'll need to lay low for a while."

Hisashi made a sad growling sound.

Izuku asked, "Does All Might still have his quirk?"

"Judging from how he's punching his way through the upper story right now, I would say yes." Inko shrugged.

"Every part of that sounds like great news," Yuuto said as Inko untied him.

Izuku massaged feeling back into his sore wrists. "You're taking this calmly, Mom. I know Dad's transformation must be a huge shock. Are you all right?" In Izuku's eyes, Hisashi as a cat solved many problems, but he did worry a little about how it might affect his mother.

Inko smiled. "I vowed to stick with your father through good times and bad ones. And cat transformations must be covered under good times because he looks so adorable like this!" She squealed and pressed a kiss into Hisashi's fur.

"This is temporary," Hisashi growled. "I'll definitely find a way to swap myself back."

"I believe in you, darling." Inko petted him. "Your fur is so soft. I'm going to brush you and kiss your nose every day."

Izuku couldn't resist a quick pet. "Whoa, it is soft." He could get used to this. His father was a lot cuter in this form and definitely less likely to stick him in a bank vault.

A crashing sound came from overhead, along with a distant cry of "Plus Ultra!"

"How about we get out of here?" Izuku suggested. He wanted to see All Might again, but not like this. What if being found in a villain's lair tarnished his chances at getting into U.A.?

"Agreed," Yuuto said.

Together, they made a run for the back door.

OMAKE TIME!

Omake: Hisashi Discovers the Truth

Hisashi: This explains why my "son" has been clinging to my "brother" like crazy. If it's not just a rebellious stage, then…I'll never get to tousle those cute green curls again? This time I'm killing the author for sure.

Author: Wait, put down the gun, I have good news. The age of the boy affects the maturity of the mind, so if Izuku goes back to his four-year-old body he should start acting like a child again. He'll want hugs.

Hisashi: I've got to swap them back, immediately! No time to test the equipment first!

Author: (Light Yagami face.) Just as planned.

#

Omake: Blame Game

Hisashi: It's all my brother's fault I ended up stuck as a cat.

Yuuto: Excuse me? You're the one who didn't notice the cat until it was too late.

Hisashi: You distracted me!

Yuuto: You didn't know what you were doing with that machine! It's just pure luck that I didn't end up in the cat!

Hisashi: If only. Just thinking about it makes me full of regrets.

Yuuto: I'd hit you, but you're just too adorable like this. Come over here and let me pet you.

Hisashi: Put me down! This is not dignified! Why do you only want to hug me now, when I don't want you to?

Yuuto: The fur…so soft…I can't resist touching it!

#

Omake: Imagine Hisashi Saying This with Eyes Bugged-Out from Denial

Hisashi: When you said that I wasn't a part of your life in the future, you were exaggerating, right?

Izuku: Not really. By high school, I couldn't even recognize you when we met again. Fortunately, All Might stepped in as my surrogate father.

Hisashi: Ha-ha, nice try, but now I know you're just trolling me.

#

Omake: The Most Important Resolution of This Story

Izuku: Hey, Uncle Yuuto, do you have a moment?

Yuuto looks up. He's currently pouring an entire package of oatmeal and raisin cookies straight down his throat.

Izuku: I can come back later.

#

Omake: The Real Reason Why Inko Didn't Attend the Sports Festival at U.A. in Canon

Izuku: I got a recommendation for U.A. from Principal Nezu? Mom, how did you manage that?

Inko: We're old friends from my animal rights activist days. He owes me a great debt.

Izuku: Uh, why does my recommendation letter say that my enrollment is on the condition that my mother never, ever visits campus?

Inko: I'm afraid the friendship went a bit sour at the end.

Izuku: Mom. What did you do?

Inko: Why do you assume that I did something? I'm the wronged party here. If it weren't for Nezu's interference, Japan's government would currently be a smoldering pile of ashes.

Izuku: MOM!

#

Omake: After Izuku Enrolls at U.A.

All Might: Young Midoriya is such a wonderful student, but for some reason it feels like his cat is trying to sabotage his path to become a hero.

Aizawa: That cat is adorable. I refuse to believe any ill of him.

All Might: The cat keeps eating his homework—and I know he's not making it up, either, because I've seen it happen. I have a strong feeling the cat ran onto the obstacle course yesterday in order to sabotage young Midoriya's score.

Aizawa: Cats will be cats. That black cat is such a beautiful, proud masterpiece of nature! I just want to pet him, even once. Yet I've been stalking him for weeks and I still haven't gotten close. My cat-charming skills have never failed me so badly.

All Might: The cat hates me. He keeps coughing up hairballs into my coffee. I know what happened to my shoes wasn't an accident. There's an evil look in those feline eyes.

Aizawa: Nonsense, that's just how all cats look.

Author's Note:

After the events of "Cat Equals Sophistication Minus Civilization," Yuuto insisted that I turn Hisashi into a cat next time to be fair. It was such a great idea, I didn't even make him bribe me for it. (Yuuto has no money, and besides, I like him more than I like Hisashi.)

To quote Mystery Science Theatre 3000:

If you want to know how the cat can talk

And other science facts

Repeat to yourself it's just a fanfic

And you should really just relax

Just kidding! Hisashi can talk as cat because years ago, he picked up a vocal quirk he never really used.

How does he have All for One, you ask? He doesn't! As evidenced by Yuuto having One for All while in Izuku's body and Izuku getting it back after they swapped, quirks don't transfer during the bodyswap process. However, there's some evidence in canon that quirks contain parts of the user's consciousness, so there's still a link between Hisashi and All for One even while his quirk is inside the cat's body. Over time, Hisashi will discover he can access more and more of his old quirks through this shared connection. Then Japan will be faced with the first—and most dangerous—feline villain in history.

But that's a problem for future Izuku to deal with! I'm sure by then, Izuku will have either become a hero capable of fighting against All for One or he'll have subdued his father with hugs and affection. One of those two things.

I'm delighted to brag that tunafishprincess drew spectacularly creepy art of my eldritch Dad for One fic Father Dagon. Delete the spaces to get the link: tunafishprincess.
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With the completion of this story, my new update schedule will be:

Tuesday evening: Let Hope Not Be Lost

The First nearly died after his final battle with All for One. But All for One took his damaged body, forced him into a centuries-long slumber, and only woke him up after enough time had passed that he had no left but his brother. A battle of wills ensues between one person determined to escape and the other determined to break this resistance for once and for all.

(In other words, the premise of this story if serious instead of cracky.)

Thursday evening: Miscellaneous Boku No Hero Academia oneshots.

Sundays: Start and End with Family

After All for One conquers Japan, Izuku makes a last-ditch attempt to travel back in time to his first year of high school. But his villainous father tags along, disrupting the process and hurling them both back further in time than should be possible. Izuku wakes up in the 21st Century, stuck in his six-year-old body with a twenty-two-year-old All for One. To Izuku, this is a nightmare. To All for One, this is a second chance, not only to raise his unruly son right but to prevent his baby brother's betrayal and later death.

The First is just horrified someone copulated with his elder brother.

(Or, unabashed crack where Izuku gets a turn to be deaged since now I've done it to Hisashi and Yuuto. Look forward to it staring next week!)