AN: While I finished the book and am more or less satisfied with it. The mention of a whole training regime for Izuku, but never diving into it, has been scratching my brain for a while as I upload the next chapter each day. I thought originally to put this somewhere in the main story, but never really could figure where to shove it. So instead, I am giving it to you here as a bonus chapter/side story. Enjoy!
This takes place right after Chapter 22.
After Izuku and Bakugo were freed from their homeroom teacher's punishment for their unauthorized brawl. Izushi wanted to have a talk about Izuku's current abilities, and to be quite frank it was very surprising to him how weak his hero version was. Entering into the dorm, as the other students waved to greet him, while he waved back and blew a few air kisses at the girls on his way to Izuku's room causing the girls to fawn over him. Knocking on the door a few times which Izuku responded by opening his door.
Swiftly in one motion as the door was opening, Izushi pushed the door aside and made his way in before Izuku managed to fully open the door. Izushi's forceful entrance caused the door to swing quickly and caused Izuku to lose balance and swung with the door as it slammed into his face while the door knob jab his gut causing him to double over in pain. "Seriously, you're actually in pain from just that?" Izushi spoke cluelessly, while helping Izuku to his feet. "What was that for?" Izuku said while still holding onto his stomach where the door knob had slammed into.
"Just judging you.." "Judging me? For What?" "Do you want the truth or the sugarcoated version?" Izushi responded in a very cold tone devoid of any warmth causing Izuku to stiffen up. Izushi relaxed himself, with both hands behind his back and looked directly at Izuku who stared back unsure of what was going on. Izushi simply smiled, but in a brief moment as the two looked at each other, Izushi left hand quickly slashes Izuku neck, cheeks, and forehead in a very shallow cut. After the slashes, Izushi held the knife out as he dropped a drop of crimson onto Izuku's lap from the tip of the knife.
Izuku was still racking his mind around what just had happened, but reacted when he saw the knife and instinctively took a defensive position inside of the room. "Tch. 4 seconds. I could have killed you 3 times with that first attack." Izushi stated as he tapped on his own neck, cheeks, and forehead to tell Izuku where he was wounded from. Izuku was sweating from the sudden attack that he wasn't expecting, but only just realized the reality of what Izushi said before about being a villain from a different world and how damn good he was. Still stunned from the shock of the attack, Izuku held his position. "Oi, Earth to Deku!" Izushi said as he threw one of the All Might action figure at his little brother causing Izuku to snap out of his trance and quickly catches the limited collector figure to avoid it being damage before blasting out a earful of complaints at how he just barges in and tried to attack him.
"That's because you're weak, and naive." the simple words stung at Izuku as he quickly shut up, and looked down slightly depressed. "I can fix the weak part, but the naivety is on you to figure it out." Izushi said, causing Izuku to look up in confusion which frustrated Izushi. 'Do I really need to spell it out for this kid?' he thought, "I am saying, I can help you get STRONGER. So do you want it or not?". Izuku's eyes sparkle at the idea of getting stronger and potentially having greater control of OFA. "I take it as a yes?" Izushi said while Izuku was nodding repeatedly.
"First thing first, show me one of your hands and get something to bite on." Izushi said as he confuses Izuku. Izuku grabbed one of his shirts and put it in his mouth while showing his right arm to Izushi. Izushi took his arm, and opened up his brother's hand while using his own quirk to look through Izuku's internal structure as he notices several malfunctions and potentially permanent injuries from his brother's previous usage of OFA reckless uses. Letting out a sigh, as he spoke, "So I am going to give you a gift from me to you, but it is going to hurt like hell. Ready?" to which Izuku nodded albeit a bit hesitant as he wasn't sure what was going to happen.
Both of Izushi's hands started to morph into various strings of muscle fiber as he dug into Izuku's hand. The different fleshy fiber attaches itself to various parts of Izuku's hand, from skin to nerves and his muscles. Izuku could feel tens of sharp needles penetrating his flesh, the worst was the fiber that has attached itself to his nerves causing indescribable pain. "Breath slowly." Izushi instructed. Next Izuku could feel another surge of pain stemming from the hand that Izushi had attached himself to, as he spread throughout his body. Izushi pumped into Izuku new stem cells as well as additional life force that he had taken over the past months to re-enforce his body. Izushi also used his quirk to forcibly tweak Izuku's DNA to restructure his body to regenerate its own cells and produce new STEM cells by itself, as well as making his body much more resilient to all types of things.
After a minute of the surgery, Izushi detached himself from Izuku. Izuku freed from Izushi, curled up into a ball with tears streaming down his face. The feeling of puking was surging up, but it wasn't quite enough for him to vomit. He had a massive headache, while every inch of his body hurt in more ways than he had ever thought was possible. The pain persisted for another 3 minutes, until it suddenly subsided.
Izuku uncurled himself, as he looked around himself to see Izushi looking right back with a smirk. "Well it seems the treatment went well." "What did you do to me?!" Izuku demanded to which a finger was pointed towards the mirror. Izuku walked over, but as he was walking he felt light as a feather, and the soreness he felt from his daily training was gone. Upon closer inspection from the mirror, he notices that the cut he had when Izushi attacked him was gone, but not only that. His previous scar from his fight with Muscular was gone, and the scars of when he broke his limbs using OFA was also gone. Looking bewildered and seeking answers, Izushi spoke up, "I went ahead and fixed some problems you had, and did a few extra. Hope you like it.". Izuku ran and hugged Izushi, "I did also fix your tendons, you don't have to worry about any permanent damage anymore. Still don't be too reckless or else Inko will get mad at me." he added.
"So is this what you mean about making me stronger?" Izuku asked after taking a step back while smiling. "No you idiot, just fixing your body doesn't mean you're suddenly stronger. I am still going to put you through hell of a training that would make Aizawa or All Might's teacher look like a trip on the beach." Izushi said, smiling back as he placed his right hand onto Izuku's shoulder to which the other boy started to shake uncontrollably.
Later that day
The two green beans were outside doing some training as it was the weekend and the one green bean didn't have any class that day. In the training field, one of the green beans was panting heavily while also had many bruises across his body and a trail of red blood dripping off of his left face. While on the opposite side the other green bean, was taking a drink out of his flask, while taunting the other to continue. As the two spar with each other, Izuku repeatedly tried to launch series of punches and kicks at the highest output he could manage without breaking his limbs, but all were seemingly dodge by Izushi's inhuman speed as he parry the attack with a half hearted wave of his right hand while holding his whisky filled flask in his left. Once Izuku was completely worn out, he was given a small break.
Izushi tosses an old book, and a protein shake at Izuku. Izuku catches both, but read the old book which was titled, "Traditional Martial Arts". "On your own time, read that and practice everything inside of it." Izushi said calmly without a hint of being worn out from the intense sparring match. "How the hell are you not worn out?" Izuku said without stuttering despite being so tired. "It's because your attack was so slow, and you were filled with openings. Your guard sucked, I even let myself be wide open for several counters all of which you never took because this school or rather society forgets about its long history before the arrival of quirks." Izushi said to a surprised Izuku as his interest in the book piqued.
After the short 15 minutes break was over, Izuku dreaded what they were going to do next as he felt all the muscles and bones in his body rattling from the fatigue. Izushi instructed Izuku to start with simple exercises such as squatting and doing push ups, but this was all too simple and something was up. To Izuku's thought was right on the mark, as he was doing his push up he felt heavy, as in extremely heavy as if a 1 ton weight was pressing his entire body downward making him choke. Being unable to take the pressure he instinctively activated OFA to try and counter the pressure being exerted onto him.
"Oh so you can handle this much, let see what your limit is." Izushi said in a taunting tone while crouching down in front of Izuku with a sinister smirk on his face. Soon the pressure Izuku felt was increasing causing him to increase his output to 10%. "Not bad, this should be about 3 tons of gravity. Let's see how long it takes to turn your bones into dust." a smile formed on Izushi's face as terror struck Izuku.
While the two brothers were having a special bonding time, they were interrupted by a candy cane and a wild dog. Both noticed Izuku seemed to be struggling to do a simple push up and that Izushi was asian squatting in front of him. The two boys approaches closer as they were curious at what was going on, "WHA-" was all that Bakugo manages to say as both he and Todoroki who step a bit too close felt immense pressure being exerted onto them as they quickly body slam onto the dirt creating a small crater.
Upon hearing the crash behind him, Izushi releases the pressure completely allowing Izuku to have a breather while both boys who approach were still on the ground eating dirt. "Don't you know it's a bad idea to get close to someone when they are training?" Izushi snickered at the blond and dual-haired boys. After some explanation to the two and hoping they would leave Izushi and Izuku alone, they instead asked if they could join to his disbelief. Izuku chimed in, to tell Izushi that they aren't going to take no for an answer and thus the two ended up joining Izuku hellish training. Bakugo and Todoroki did similar workouts to Izuku, however the pressure that Izushi exerted were expertly controlled to fit each of their training.
By the time they stopped, it was about time for dinner already as they all headed back to the dorms and Izushi left to go back to his apartment. The rest of the week, Izushi would train the three of them as other students started to take notice and watch from a distance, some snickering and acting as if it was a simple task to which Izushi threw a tennis ball at them and knocking them on their ass while also causing them to black out. The training continued, but because of Izuku getting special treatment prior to the actual training, Izushi was particularly harsher. Izuku had to withstand strikes from Izushi, which tore off a bit of skin, muscle, and fractured his bones. Occasionally Izuku would receive such severe damage that others who watched could see Izuku's exposed bone. All Might, Aizawa, and Nezu tried to intervene, but were blocked by Izuku as he said he wanted this training. They were also forced to back off as Izushi was already annoyed at them for the weak level of heroes that was being developed at the school, since he released a bit of bloodlust and it was enough to shut them up.
Recovery Girl, who was relaxing in her office, was interrupted by Class 1-A asking how Izuku had been doing the past few days with his horrendous injuries from his training with Izushi to which she was clueless on. Arriving, shortly after Izushi shut the three heroes mouths, she voices her disapproval of the training and tries to scold both green beans. Izushi, who understood her perspective, grabbed Izuku and caused his injuries to rapidly heal before all of the spectator's very eyes. "Happy now people? Yes? Good, now please be quiet and either watch or get lost.".
Without waiting for another word, Izushi resumes, and Izuku attempts to dodge the various blows, and block others. He felt his body quiver in pain, but the adrenaline was overwhelming him as it was exciting, his body has quickly adapted itself to OFA and he has already achieved natural control of 40%. All Might stood there speechless as well as Nezu who were in the know about Izuku. Nezu fears how strong Izushi actually was, and wishes that Izuku never become a villain like Izushi was in his original world. It was from his observation that he concluded that Izuku must stay on the hero path no matter what, and the other part was the ominous feeling he felt from Izushi and the day of the Kamino Incident that kept ringing alarm bells inside of himself.
Izuku throughout the training manages to dodge more and more hits, while successfully blocking attacks without his bone shattering. His body rapidly adjusted itself to be able to withstand the monstrous strength of Izushi's attacks. It was getting a bit late, but everyone was still watching the fight. Both Bakugo and Todoroki were watching everything very closely. In a single moment, whether it was pure luck, or Izuku finally manages to read his opponent. Izuku landed a 60% OFA punch directly into Izushi's face, forcing him to slide back several feet. His body rapidly mutated its internal structure to the stress being exerted on itself through the training and fight throughout the week causing him to rapidly gain more control of OFA.
Quickly recovering from the injury, Izushi spit out some blood that pooled in his mouth from the hit, and dusted himself as he approached Izuku who was in a defensive stance still and fully on guard for any surprise attack. To Izuku's surprise, the attack he received was one he least expected. Izushi grabbed him in a bear hug and congratulated him on successfully passing his training with him. The two celebrated by heading back to the dorm with the rest of the class and Izushi cooked up a feast for everyone to enjoy. All the while the pro heroes are still trying to wrap around what they saw throughout the week of Izuku's training with Izushi, in both fear, and amazement, but a whole lotta fear at how strong Izushi was.