All for One's hand came down and wrapped around his head. The levitation quirk he'd manifested had cut out, causing him to fall back down to the cot below him. Izuku wanted to lash out, but the very recent electrocution had him feeling weak and twitchy. "I suppose we'll start with this one."

After one quirk, Izuku felt bloated and nauseous, like he'd eaten way too much but was still starving. It made his skin tingle and the pain of it was manageable, like licking a battery. It didn't take a genius to tell it was some sort of electricity quirk, but he couldn't tell what it did exactly.

"Hm, seems like you took to that one quite well, though emitters always are easiest on the body. Let's see how you handle a transformation quirk."

He was pretty sure there was some sort of paralysis quirk that kept him or Tanaka from moving at all as he felt his body adjust to the additional ability. This one hurt. It felt like he was speedrunning a fever, feeling way too hot and cold all at the same time. It was like being burnt alive and frozen simultaneously, even though that didn't make any sense. Possibly a temperature or energy conversion quirk?

"Some resistance on that one, but your body was still able to adjust. You didn't seem to feel any pain from manifesting your levitation, so that implies your quirk treats them as secondary effects, rather than independent quirks since gaining additional quirks clearly puts stress on your cells. You truly are a fascinating specimen."

Specimen.

That's all he was to this man. The father he'd longed for his whole life, who turned out to be some immortal boogie man, saw him as nothing more than a particularly interesting object to investigate. It left him feeling like a frog being dissected by curious kids in a science class.

The third quirk made him scream in agony as if his body was ripped apart and rebuilt over and over. He didn't have any sense of what was happening other than the overwhelming feeling of his bones being crushed. There were no more thoughts or guesses on what it could be, just all encompassing pain.

The scream has a dissonant sound to it as Izuku and Tanaka cried out at different pitches through the same vocal cords. Both of them felt the excruciating pain as their shared body was altered to the whims of a madman.

"Interesting, your body was able to adapt to the new quirk without any real issue, but your original quirk didn't protect you from the pain of the change. From what my spies have told me, you have quite the interest in quirks, so I'll let you in on something I find intriguing. When I make contact with a person, I can sense the quirks I can take. This means my quirk reads you, my brother, and a few of your siblings as being quirkless even though that clearly isn't the case. Even as I give you more quirks, you still appear to be quirkless because I wouldn't be able to retrieve them from you. Isn't that fascinating?"

Izuku's body began to spasm and twist in a pitiful fight against the new quirks that were remaking him at a cellular level. He held out for a few more seconds as he screamed and sobbed before falling unconscious.

Izuku woke back up to a large laboratory and a deep ache in his body. He looked to the side and saw a surprisingly familiar face. He blinked a few times to make sure that it wasn't just his groggy brain tricking him.

His voice came out scratchy and weak. "Dr. Tsubasa?"

"Ah, you're awake. Don't mind me, I've just been updating your medical files and took some samples to see if it would be possible to duplicate your adaptation quirk. So far it seems like that won't be an option, but I've never let a seemingly impossible task scare me off before."

"...Why?"

The doctor was still looking down at a clipboard and filling out some form. "At this point I've found it to be impossible to duplicate quirks that are sentient to any extent."

The doctor paused for a moment before realizing that wasn't what Izuku had been confused about. "Oh, I imagine you're surprised to see me since you only ever saw my false identity of Tsubasa. My actual name is Daruma Ujiko. That role was just for collecting quirks and watching the development of his children. I must admit, I never expected you to be the shining star of the bunch."

Izuku winced a little as a man shined a bright light into his eyes without warning. Izuku felt Tanaka stir and whispered to him, "I've been up for a bit, but there's not a lot we can do right now, let's wait and see what we can learn." He felt his head turned to the left by Tanaka where he now saw at least a dozen Noumu standing guard. And even if he somehow got past this mad scientist and the monsters, the cameras aimed at him would likely notify his father the moment he made a move. He supposed there was also the issue of being strapped down to the table.

The doctor continued talking casually as he began another test, for the moment it seemed to be another harmless one as various X-rays were taken. "It's almost funny, I really expected the Nakamura girl or the Kudo boys to take my master's place one day with the power they had, while you were a meek little quirkless boy the last time I saw you. But those boys have suppressed their quirks for nearly a decade living with some civilian family, and Nakamura pretends her quirk is so much weaker than it is for the sake of fitting in."

He paused for a moment in thought. "Now that I think of it, you probably know Nakamura, but she's been going by Suzuki ever since she got taken in by her grandmother. A real shame, her mother was probably our most devoted carrier."

Izuku was shocked at this revelation and barely croaked out a response, mostly ignoring the horrible way the doctor spoke about people. "Suzuki is my sister?"

"Half sister, but yes. I had assumed you already knew about your siblings, but if not then I suppose you'll be finding out soon. As I was saying, her quirk is so much more powerful than she says. With a single touch she can manipulate all the muscles in a person's body for the next few minutes. Which means it's both a powerful puppeteering quirk and a one-touch-killer quirk, but she pretends it's a cramping quirk just to fit in."

He waved his hand through the air. "But I could talk about the results of the quirk farming all day, organizing the stock to create the best quirks was always one of my favorite jobs. What we need to discuss are your quirks so that you can use them properly and serve your father well."

Izuku was skilled at many things, keeping his mouth shut to save his life wasn't one of them. "I'm never going to follow any villain, let alone him. I don't care what you do, I'm not becoming his 'successor' or whatever else he wants from me. Your experiments are disgusting, immoral, and I look forward to putting a stop to them."

He could feel Tanaka panicking and preparing for a fight, since provoking a mad scientist while in his lab wasn't exactly a smart plan. But the man just chuckled.

"I have been the right hand man of your father for just over a hundred years now, and I have seen countless people proclaiming that very same thing. Actually, I think you'd benefit from a demonstration so you better understand the situation. Let's go on a quick walk."

The metal cuffs holding him down suddenly released, letting him move freely. He heard Tanaka whisper in his ear, "This man is clearly insane and sadistic, I think we should take him down before we reach this 'demonstration'. Plus, the nomu need verbal directions, right? So if we get rid of him and run, we might get out of here before the big guy finds out and shows up."

It was risky, but they didn't have a lot of good options. He slowly stood up and nearly fell from how weak his body felt.

"Ah, you can use your IV stand as support. Gaining so many quirks was very taxing for your body."

He was in enough pain that he hadn't even noticed the IV in his arm. It wasn't in place either, every single cell was sore from being altered in one way or another. Every step felt so heavy, like his feet were made of lead.

"That's quite close to the truth, actually. You now have the quirk 'Steel Bones'. I do find it amusing that you still have a problem with mumbling after all these years, however, you'll need to get a handle on that if you're going to be a decent successor. Let's walk and talk, I'm a very busy person."

They moved further and further into the strange laboratory filled with the nomu containers and a weird amount of pipes tying everything together. Each pod had a half formed and badly deformed body inside. The entire lab was a grotesque example of what science could do when not constrained by law or morality.

"The quirks you received are intended to cover any obvious weaknesses you had. Your bones kept breaking from not being able to keep up with your power output, so we changed them to steel. The slime aspects of your body leave you vulnerable to cold temperatures and electricity, so now you can regulate your body temperature and absorb electricity. You also received the standard copy of a regeneration quirk." The man laughed a bit to himself. "We wouldn't want you dying on us, now would we?"

"Now, the last quirk you were given is a surprise. It's a passive one though, so you don't need to worry about training it or anything like that. Ah, here we are."

They stood in front of a large container that glowed purple, and floating inside was the body of Muscular. He could see the bullet holes from where Momo shot him and the empty socket that used to hold his prosthetic eye. He was clearly very, very, dead, but at the same time his one remaining eye tracked them as they moved closer.

"This man was stubborn and prideful to the point I doubt he would have ever bowed to the power of my master. Yet here he is, completely loyal without the willpower to even consider disobeying. Give me a few months and he'll be stronger than any hero, plus he'll finally follow orders." He turned and looked at Izuku. "So you need to ask yourself. Is this the fate you want? Because right now you have two options, follow your father of your own free will or follow my commands as an animated corpse."

Izuku just stared at the man in terror before Tanaka responded. "How about neither, you piece of shit."

A tendril of slime tipped with a steel blade shot forward and sliced the man in half with a single blow. "Alright, we need to get out of here now, I don't know how much more fighting I can do so we can't wait for reinforcements."

Izuku nodded and did his best to pick up his pace when he realized that the mad scientist hadn't turned into a pile of blood and guts but a pile of mud. "Tanaka somethings wr-"

"To be honest, that took you longer than expected. I expected you to strike the moment we stepped into the hall away from my Nomu, or maybe even as soon as I undid you restraints." Although the voice was just as chipper, the fact that the man could still speak was bone chilling on its own. They both looked over to see an identical copy of the doctor walk over.

"I hope that both muscular and that little attempt have been a good lesson. Pride will get you nowhere. I won't stop you from rebelling though, I personally would prefer you get yourself killed and end up in my lab again. Make your choice Izuku, Tanaka, become your father's successor or my crowning achievement."