Deku awoke in the familiar sheets of the U.A. Infirmary, the familiar smell of disinfectant in the air. He felt the familiar sensation of his muscles screaming for a longer rest and the familiar annoyance that his body still wasn't used to his... extreme lifestyle. Yet when he opened his eyes, he was met with an unfamiliar sight: two students at the foot of his bed, both eyeing him with unease and anxiety. Or rather he wasn't used to seeing this sight immediately upon waking.
"Ms Hado, Mr Amajiki." Immediately they were on guard.
"Don't you dare move," Neijre Hado said, hands outstretched and ready to launch her signature lightning.
"Yeah, just... stay there," said Tamaki Amajiki, his arms outstretched and fingers extended to form squid-like tentacles. "Don't try to hurt Mirio again."
"Relax, I won't," Deku said, closing his eyes for another few moments of rest. "He's already proven himself worthy of being U.A's number one. I look forward to seeing him in action."
"Well it's too bad you'll be in jail when he becomes a Pro Hero, isn't it?" Ms. Hado answered, her arms never moving from their 'standby phase'.
"No, he won't," came a voice from the doorway.
"Sensei," Mr. Amajiki said, surprised at Aizawa's appearance. "Wait, what do you mean he won't be in jail? He attacked Mirio."
"Yes, to test his strength and ability to be a hero." Aizawa turned to face his colleague, who was intently listening to the ensuing conversation. "Since you evidently aren't aware, this is Deku. He is a teacher of Class 1-A and 1-B, and a... retired villain."
"WHAT?" Ms. Hado exclaimed. "He's the villain teacher?!"
"That's correct. He appeared as a villain to make sure Mirio wouldn't hold anything back against him, and ensure he would see Mirio at his full strength."
Recovery Girl, who'd been typing away at a computer for this time, sighed in exasperation. "I wish you'd have told Aizawa about your plans beforehand. That said, I'm not surprised by them. At least you bothered to tell me about them and prepare two beds for you."
"So he's the villain teacher, huh?" spoke the face above Deku's bed. Everyone jumped back in shock. "Relax guys, it's me," Mirio added, emerging from the wall. As Recovery Girl shuffled over to try and get him back into his bed, he turned to face his ex-opponent. "You know, when I saw you yesterday I thought you were a student. You look so young."
"Well I am about the age of most first-year students, so that makes sense," Deku said, nonchalantly.
"Woah, really?" Mirio asked as he disappeared behind the separation curtain between their two beds. "I never would have expected such a powerful individual to be so young."
Have you seen yourself lately, Deku thought to himself before replying, "Well that makes two of us. You really got a second wind near the end, didn't you? If I didn't know better, I'd think you had a strength-enhancement quirk of some sort."
"Huh, it wasn't that impressive. I just... couldn't bring myself to accept defeat."
Deku smiled. "An unwavering will is very impressive. In most cases, it's extremely stupid to have since most people don't have the strength to back it up and end up getting themselves killed. You, however, have refined your quirk so well that you can afford to keep fighting against even the most powerful of villains without being squished like a bug."
"Indeed he can," came a new, weary voice from the entrance.
"All Might!" Mirio cried out as All Might entered the room. "You came to see lil' old me?"
"Of course. I heard about your little encounter with Deku here and I just had to come and see you both." All Might handed them both a bottle of water he'd picked up on the way here. "So how'd it go?"
"He's extremely powerful," Deku answered. "Even though we were both rendered unconscious by the end of the bout, if he had gone all out from the start, I have no doubt I would have lost." You chose a good kid to be your successor, Deku tried to convey through his eyes to All Might. He seemed to understand that Deku was trying to say something, but not exactly what. Eventually, he just gave a nervous thumbs-up and gave up guessing. Annoying, but so be it.
Eventually, the Medical Room started to empty of its visitors, but before he left, Deku called over to All Might. "Hey, All Might. Do you mind if we have a chat soon? About..." he looked around to make sure no one was listening "... about Mirio's condition?" All Might looked confused for a moment before a look of realization crossed his face.
He looked over at the boy, who had fallen asleep a few moments prior. "All right. We'll talk soon." And with that, he left the two boys.
He really cares about this kid, Deku thought to himself, and not just because he's the new wielder. He's acting like a father taking care of his overly ambitious son. I wonder if he'd treat me like that if I was One For All's wielder... And with that thought, he closed his eyes again, allowing his body the rare opportunity to sleep. Not meditate, not fall unconscious, actually let down his guard and rest. He didn't admit it to himself or anyone else, but... he needed this.
A Few Days Later...
All Might was on his way to his office when he met Mirio heading in the same direction. "Mirio," All Might began. "I'm glad to see you out of the Medical Bay."
"Yeah, Recovery Girl wasn't happy. But as long as I go easy on myself for a while, things should be fine." Mirio laughed it off, but All Might could hear the wheeziness in his voice, and see the pain hidden in his eyes. He knew it far too well.
"Well that is good to hear," All Might said, smiling a comforting smile. "Hey, if it isn't too much trouble, could we have a quick talk?"
"Sure. What about?"
"About...uuh..." All Might couldn't find the right words, so he just finished with, "... I think it'll be easier to explain." And with that, he set off to his office, Mirio in hot pursuit. When they reached the office, All Might opened the door to find Deku sitting on the sofa by the coffee table, sipping a cup of warm tea.
"You're here," he said, calmly placing his teacup on a coaster.
"How long have you been here?" All Might asked.
"Not long. Only about 5-10 minutes or so. Shall we get started?" He asked, getting up from the sofa and offering his seat to the two.
"Yes. Let's get right into it." All Might walked over and sat in the armchair at the head of the coffee table. "Mirio, we need to talk... about One For All?"
"One For All?" Mirio asked, eyes wide in mock confusion. "What's that, professor?" he asked, lurching his head in Deku's direction as if to say, He's right there!
"Relax Mirio, I know all about One For All," Deku responded to the head jerks, going for another drink of his tea. "Although he never showed it, All For One was obsessed with it. As a result, he tried to create a database concerning properties, strengths, weaknesses, and current wielder of it, and even though I'm not primarily a hacker, I still know my way around a computer."
"And so you understand why word of One For All can't be leaked to the public, right Deku?" All Might asked, a silent plea for help in his voice.
"Of course All Might," Deku answered. "I won't tell a soul that Mirio is the current wielder." Both All Might and Mirio breathed a sigh of relief at that. "On the plus side, it can't be taken by force, so-"
"It can't?" Mirio asked.
"No, it can't," Deku answered. He then paused, before turning to All Might. "How much have you told him about One For All and All For One?"
"Enough to get by," All Might answered. "Given the current climate, I planned to tell him everything today."
"Everything on what?" Mirio asked, the usual carefree smile absent from his face.
"Everything on the history of All For One and One For All, of course." Deku sat back on his sofa. "Take it away All Might," he said, before leaning back and letting All Might explain to Mirio who All For One is, what One For All is, the nature of its creation, and, in essence, its purpose.
"It's a lot to take in, isn't it?" Deku asked once the explanation was over.
"So, One For All was created by All For One?" Mirio asked, still trying to understand.
"Unintentionally, but yes," All Might answered. "He gave his brother the power to store kinetic energy within his body. The brother already had a quirk, however it had no effect, only guaranteeing that it would be passed down to a new wielder. These two quirks combined, allowing the user to store up kinetic energy and release it, as well as passing on that ability and energy to a new wielder. This power has been passed down several times in the past. You are the ninth wielder of One For All, and as its new wielder, you must continue to fight back against All For One."
Beat.
"It has a... scary past, doesn't it?" Deku asked, looking up from his meditative state.
"Yes it does," Mirio answered, looking down at his hands and chuckling.
"As with all other information concerning One For All, this is to remain between the three of us and only the three of us. Alright?" All Might declared, with which he was met with nods of understanding.
"So how far can he go without blowing up?" Deku asked.
"The furthest I can go is 45%, but I can only hold that for short periods," Mirio answered. "Honestly, most of the time I don't need it, but when I do use it, I tend to maintain around 25-30%."
"45%, huh?" Deku answered, impressed. "That's quite remarkable. Anyone else would probably be at about... 15% or so at this point. Consider me impressed."
"Thanks, Deku," Mirio responded, the bright smile back on his face. "Do you wanna see me at my strongest?"
"Hmmm... sure, why not?" Deku answered, ignoring All Might's pleas. "I want to see the current extent of your strength."
"Alright," Mirio said, standing up. "45%!" With that, his body began to spark, small bolts of golden lightning arcing from his head to his toes. Waves of energy pulsated from him, making Deku's hairs stand on end.
"Incredible," Deku said. "The fact that you are radiating energy proves your strength."
"I can even create-" Mirio began, beginning to walk towards Deku. Unfortunately, due to the kinetic energy stored within him, the movement of walking created great waves of air pressure. The result was the equivalent of a dry storm in the middle of the office, throwing papers everywhere and knocking ornaments off of All Might's desk.
Eventually, the pressure died down, dissipating until all that was left of it was the papers that were wafting down from the ceiling.
A brief silence.
"I probably shouldn't have done that," Mirio said, nervously scratching the back of his neck.
"Do you want to help clean this up?" All Might asked, gesturing to the chaos resulting from the mini-typhoon.
"Yes," Mirio immediately answered, and all three of them began to clean up the mess that Mirio had caused.
Abilities acquired:
Bloodlust: increases violent thoughts, speed, and reflexes but decreases rationality whilst active.
Extrasensory: increases sensory sensitivity but reduces motor skills and physical ability while active.
Mania: suppresses all negative emotion and empathy while active.
Whirlwind: increases speed and reaction time but decreases upper body strength while active.
Combos:
Psychotic Cyclone: massively increases speed, reflexes, and reaction time to godly levels, but massively reduces all other forms of strength while active.
Devil Incarnate: massively increases speed, strength and reaction time, but reverts the human to an animalistic state obsessed with killing whilst active. The person will also feel trapped and unable to move whilst visions of death appear before their eyes.
Wind Spirit: increases speed and reaction time to enhanced levels whilst also granting an enhanced awareness of the users environment. The user has decreased upper body strength whilst active.