Kyudai Garaki, also known as the Doctor, is a villain affiliated with the League of Villains. He was a faithful servant of All For One and later to Tomura Shigaraki.
At the same time, he was also the doctor who told Midoriya that he was Quirkless, and had a shock.
If there was a reason why someone as bright as him would dedicate himself to the villain, All-For-One, it was because seventy years ago, Kyudai theorized the "Quirk Singularity", according to which, as the generations pass, the Quirks will become so powerful that they will be uncontrollable. However, his theory was dismissed by society, which viewed the concept as ridiculous and didn't want to listen to a far-fetched doomsday theory when society was still struggling with assimilating Quirks into society. As a result, Kyudai was ostracized and disappeared from the public eye.
Left alone and with nowhere to go, he eventually discovered All For One and approached him about the theory, who believed him and lent Kyudai his aid. It was then that Kyudai began working with All For One.
Still, among all of Kyudai's research, instead of the Quirk Singularity, Sato was more interested in the Quirk Duplication.
Yes, through advanced scientific means to copy a person's Quirk and preserve it in a container, allowing the possibility of transferring said ability to another individual.
While it took a lot of time to duplicate a Quirk, Kyudai had already duplicated a few of All-For-One's Quirks, and if Sato wished to, he could put that Quirk into his body with the help of Kyudai.
So, should he do it?
Still, this also put him at ease, as this method was quite acceptable, as it was quite similar to the Evil Piece, which reincarnated Sato DxD into a devil.
Sato wasn't unfamiliar with the concept of body modification, and frankly, this Quirk duplication process was quite similar to the process of the Evil Piece, reincarnating any living being into that of a devil.
Frankly, this was just his hypothesis, as he didn't have any evidence of this, but he felt that the world of DxD had been destroyed once.
Yes, it had been destroyed, and all the traces of that world were those of the lost technologies discovered in various mythologies, including those that were found by Ajuka in the Underworld.
In that world, whether it was magic or science, everything had reached its peak, something that no one could have imagined, but somehow, it was destroyed, and the world became what it was, missing something that should have existed.
As for why it was destroyed, Sato wasn't sure, but regarding the God of the Bible's ability to create the Sacred Gear, its system, and various other things, he felt that it was related to the destroyed civilization.
Still, with this, he had made up his mind to put the duplicate Quirk of All-For-One into his body, yet—
"Are you okay with that? This is a dangerous process!"
As Kyudai was under Sato's hypnosis and mind control, it was natural that he cared about Sato's well-being.
"It's fine."
Sato knew his body well, and it was so durable. More importantly, as he thought of Sato DxD and his Sacred Gear, Twice Critical, it made him think of a certain possibility.
So, without hesitation, he made Kyudai take him into the laboratory to do this operation.
As for All-For-One, he could only sigh since it seemed that Kyudai didn't even know where he was.
All-For-One didn't even tell where he was to his most trusted follower, which made Sato understand why this guy could live for so long till now.
'How old is he again? 120 years?'
Sato somehow understood why this guy was called the last villain.
"Please come inside there. I will do the surgery for you."
"Thanks."
As he was inside the sketchy laboratory on the underground of the hospital, he couldn't help but look around, watching various creatures that were inside the experiment tube, floating inside a certain type of liquid that he wasn't sure of.
"By the way, what are they?"
"Oh, that's Nomu. You can say that they are robots that I have made by using corpses."
"Like that of necromancers?"
"Yes, that's the best example!"
To raise the corpse from the dead and fight for the owner, Sato thought that this was what Kyudai had done.
This guy might be a little strange, but Sato understood why All-For-One loved him so much that Kyudai would still be alive till now and be well-protected.
Still, because of that, Sato also thought to use Kyudai as well. His talent was limited, and instead of relying on himself, he should have relied on others, so they could help him with his ambitions.
"Everything is set. Are you ready, Master?"
"Yes."
Sato entered the chamber tube and felt his body become weightless as he was inside the liquid.
"Start."
"Yes!"
Sato made a sign with his eyes, and Kyudai started the surgery.
Yet, while the two thought the process would be painful, it was strangely calm and not even painful.
Sato felt like a missing part of his body had merged like a missing piece of a puzzle that he thought he had lost.
"A-Amazing!"
Yet, Kyudai, who saw the data, felt like he had been thunderstruck, feeling like he had seen a miracle!
"100%! No, it is more than that! It's my first time seeing something like this! Wow! Wow!"
'As expected!'
Originally, one person could only own one Quirk, and more than that, their bodies couldn't bear it, and they would be broken apart.
It was like the previous users of One-For-All, before All-Might and Midoriya, who had their own Quirks except for One-For-All, had all died early and broken apart. Naturally, there were many cases where, as the human body, while it was full of potential, it had a limit, and once that limit was exceeded, their bodies would be destroyed because a limiter exists within the human body.
As for All-Might and Midoriya, the two of them were Quirkless; they had no Quirk, so One-For-All could fit them well.
Yet, Sato was different; he had the Twice Critical!
His body was built so he could accept two Quirks!
The concept of double!
Sato DxD had worked hard to reach that power, and because of that, Sato MHA could accept the Quirk of All-For-One inside his body.
Naturally, unlike Shigaraki, the villain of the MHA, who almost lost control over himself due to All-For-One, Sato had no such problem, as what he received was just a duplicate.
Still, even if what he got was just a duplicate, when it was enhanced with the Twice Critical or trained further by him, would it work less than the original?
As he thought so, the surgery finished, and he came out from the chamber under the worship gaze of Kyudai, and at the same time, he also gained the new Quirk, known as All-For-One.
"Now, how about we test it?"
As he looked at Kyudai, he showed his best, gentle smile.