A/N: Some OOC here and there because this is a Traitor AU.
Also, prologue. Because we can't get into the fun without exposition!
It was about that time again. The time to visit his godfather in his ash-scented, sewer-like briefing room.
Shigaraki Tomura paced around the empty boss chair, taking in the sight of the four mossy metal walls that made up this room. There were no doors or windows or any signs of a way to exit. This was an enclosed space with rusted oxygen tanks held against the floor. The oxygen tanks were there to fill the room with breathable air, because there was no ventilation system. It was also not at all spacious because it was six meters squared in area. Nothing could come in or out without the use of a porting Quirk and the knowledge of the location of this room. Basically, only two people could access this place.
All For One and Kurogiri.
And also Tomura, in the extent that he knew the location but had no sole means of travel.
As Tomura walked around the back of the chair, he heard the sound of thick liquid dripping in the soundless room. He stepped to the right side of the chair and found a man sitting in it. All For One appeared to be sitting in the boss chair the entire time.
"Tomura," the older man said, "I told you to be on time."
Shigaraki stepped in front of All For One, bowing his head. "Actually, Sensei, I've been walking around for..." he stopped to look at the watch on his wrist, "...seven and a half minutes. I was early."
The powerful Villain hummed in thought. "My point still stands," All For One replied wistfully, "Always be on time. If you're early, you show that you're a bit too enthusiastic for the job, and that shows weakness. Same goes for being late: you show that you're not up for the job. Always be on time, Tomura."
The hand-themed Villain scratched his neck. He's the one who's two minutes late... He thought, as he waited for the bigger man to start this meeting. When All For One was looking down at him from his boss chair, expecting something, Shigaraki deduced that he should respond to his wisdom. "I see, Sensei."
A moment of silence passed from All For One. Tomura waited a little longer before deciding he should start the meeting himself.
"Anyway, you wrote to me a letter about some urgent news. I don't see the reason for the letter and why you wrote down such a small message, but I do believe we are about to discuss something secretive. So why don't we get on with that?"
"Oh. Right. That." Sensei tapped on the arm of his chair for a moment, deciding on his words. When he finally got them, he stopped tapping. "Well, I don't know how you would process this information. This is very exciting news and not even I believe it to be true... despite the fact that I was the one who orchestrated this certain event. It seemed too good to be true and now I'm going over it in my head if I should tell you... It might be a lie and could burden you."
"Well, since you got a pigeon to send me that letter, I'm pretty sure you've already put a bit of definite thought into it." Tomura retorted, tilting his head to the side.
"Alright. I'll say it..." All For One paused for dramatic effect, which irked the Disintegration-Quirk user. "...We have eighteen student spies in U.A. High School."
Tomura stood still, processing that in his head. It took him a while for it to register. He knew that they were gonna get a few spies in there, but not eighteen. It sounded too good to be true. Too much like a dream. This couldn't be happening, but this was really real. And he could tell because he never had dreams in this godforsaken room. There might be that one time, but it was too much of an acid trip to be classified as real. The younger man blinked, then scratched his neck.
"...eighteen spies..." he repeated under his breath, still not used to this gift of god.
"Yes. And in the same class. 1-A, they all tell me." All For One dabbed a few beads of sweat with a handkerchief. "Eighteen out of twenty students in one class, our spies."
The younger Villain was still staring at the ground, a bit winded from the information. He tried to keep his thinking straight, but one thought kept clawing out of his soul.
"Isn't this... unfair? This is too much." Tomura remarked, a bit worryingly as it made him question his beliefs as a Villain himself. "I get that Heroes cheat a lot, and you might be saying that this is our time to do so, but... doesn't it feel wrong? Aren't we supposed to be the better men?"
"Don't blame me. It happened. I had no control over it." All For One said, before giggling quietly. "I mean, I had control over recruiting them, yes. But all of them huddled in one class, no. Eighteen out of twenty. The same Heroics class," he repeated.
"No, no, the school will know. Or they already know. This won't work out for us." Shigaraki brushed his father's hand through his hair, revealing his distraught face to the ground. "They'll all be working together. Too suspicious. The other two students will figure it out and report to the school. Too many teens—variables, they will make a mistake. It's just like that law that states that anything that can go wrong, will go wrong."
"Additionally, I didn't tell them that their fellow classmates are also spies," All For One added.
"Well now they'll all be suspicious on their own..." Tomura said, before thinking of what that would look like. He could see a class full of shut-offs. That's it. Nothing particularly interesting. Which made it very suspicious. And then he thought of them trying to fit in, and the class would become so alien-like due to most of the students trying to mimic each other and be relatable to others' blank canvases. He could already see the half-assed smiles and the vague answers from this sealed room.
"We shouldn't underestimate them, Tomura. They can be better than what we think of them now. You haven't met them yet. They are teenagers in Hero training after all. They should have the capacity for intelligence if they got in. If not, then how would they have even passed the written tests?" All For One added the last bit accidentally, putting his assuring thoughts on the forefront.
"You sound like you're asking me for reassurance." Tomura shook his head. What was he saying? All For One was just testing him. Why am I worrying anyway? If they're caught, they're caught! No repercussions, except for them babbling about what they know of the League of Villains!
"You will not worry anymore." All For One commanded, and Tomura raised an eyebrow.
"How can I not? They're gonna report to us the same information at the same time. We don't have that many phones." After speaking, Tomura felt something come over him, like he shouldn't think of this situation anymore. That he shouldn't worry... His tense shoulders were becoming relaxed, and then he realized his body was doing it against his orders. In a desperate attempt, he choked out, while in a relaxed tone, "Sensei! There's something wrong going on!"
"Oh, don't worry. It's just a Brainwashing quirk I received," he stated. "It activates when someone responds to me. In this case, you spoke after I told you not to worry... which would probably shut off some of the workings in your brain. But fear not, you won't worry anymore."
Tomura nodded, drool coming out of the side of his mouth.
"Now, since you're probably braindead from a part of your brain not functioning, shall I tell you the story of how I attained such a quirk? This also ties into one of the student spies we have..."