Ultra Instinct Deku
WARNING: Before I start this fanfic, be aware that other fanfics from other people could've made the same concept and I want you to understand that I'm not copying any of them, just sharing the amazing idea. (3rd SEASON SPOILERS AND A FEW MANGA SPOILERS)
Also, there may be some OCs to the story that I just made them myself so the story doesn't have a lack of villains to choose.
This is a crazy fan idea that gives our protagonist Izuku Midoriya the amazing power of Ultra Instinct.
The story will take place weeks after provisional license exams, where Deku and his friends are able to fight villains almost freely and a villain attack will occur.
It was a sunny afternoon at U.A. High School, class 1-A students went to the training camp to strengthen their quirks again, and hoping that this time, a villain attack won't occur. Unfortunately, Shigaraki planned another attack at them.
Bakugou: DIEEEEEEE!
The young hot head exploded his hands making an enormous explosion in the air, even more mad seeing Deku improving his shoot-style even more, on the bench near the camp, there were some people resting after training, near the area, the members of The League of villains were sent to spy our heroes' training, and they weren't going to make an ordinary attack, they were going to focus on one student. The league of villains spied All-Might and Deku's often conversations, discovering that young Midoriya is important to the previous symbol of peace.
Katsuki: Hey Deku, why are you there licking the ground!? Get up and continue training, you nerd!
Deku: K-Kacchan, I was just resting, calm down!
Katsuki: Tch! How do you plan on surpassing me? Being a slacker!? I hope not!
*BANG*
Lida: Midoriya watch out!
Lida quickly grabbed Midoriya and Katsuki at the same time, dodging the bullet.
Deku: What was that!?
Katsuki: Who's there?! Show yourself, coward!
1-A soon found themselves surrounded by villains and criminals, it was another attack! In a matter of seconds, Deku noticed most part of them were looking at him, he was being tagged!
Todoroki: It looks like it's another attack, huh?
Bakugou: Wow, no shit, Todoroki.
Lida: That's odd, why are they all focusing their eyes on Midoriya?
Bakugou remembered about One-for-all and All-Might's frequent conversations with Midoriya, did the League of Villains find out about Deku's One-for-All? Impossible.
Two Nomu, the ones that previously fought All-Might, jumped in Midoriya's direction, but he quickly jumped and dodged the attack.
Midoriya: D-dammit! They are tagging me! This is bad!
Villain: Isn't it? All Might's secret love child!?
A villain quickly threw a flare burst at Midoriya, but he countered it with an air pressure beam made by his legs in shoot-style.
Todoroki: Midoriya!
Todoroki made an enormous mountain of ice, protecting Deku from incoming attacks.
Lida, Bakugou and the others hidden themselves under the mountain of ice too, planning an attack.
Lida: Why are they all tagging you Midoriya?
Deku: I.. don't know…
Tsuyu: This is awkward, why would they focus on Midoriya?
Ochako: Maybe they discovered that he comes up with great ideas and decided to eliminate the brain of the team!
Bakugou: HE'S NOT THE BRAIN OF THE TEAM!
Todoroki: Everyone, discussing the reason they tagged Midoriya isn't what we should focus on, the mountain won't last longer, we must think of a strategy!
Lida: Indeed. If they focus on Izuku, we must protect him!
Denki: Like a tower defense game!
Kirishima: I won't let you get killed Midoriya!
Deku: T-thanks…!
Bakugou: Like hell I'm protecting this nerd , I'll go all out on the villains first!
Lida: Bakugou wait!
The hot headed teen blew up one of the walls of the mountain of ice and started to blow up the villains while some of them were entering the heroes' hideout.
Todoroki: We'll have to go all out on them!
Bakugou (from far away): WOW NO SHIT TODOROKI!
The mountain broke and our heroes started to beat each villain one by one, Deku quickly hid himself in a nearby forest, searching his surroundings.
Ochako: Deku! Over here!
Deku: Ok!
Deku started to walk toward Ochako, however, he saw a knife hidden behind Ochako's back.
Deku stopped
Deku: You're not Uraraka.
An amount of slime started to slide down from Uraraka's body, revealing the naked body of Toga Himiko.
Deku: T-Toga?!
Toga: You rembered my name, Deku! I'm so glaaad!
She quickly jumped and almost grabbed Midoriya, but he quickly jumped and dodged the knife, seconds later, Himiko disappeared.
Deku: Where could she have gone to?! Dammit! I must watch my surroudings!
The ground started shaking and another villain burst from the ground and grabbed him in the air.
Villain: You're lost, young Midoriya! I touched you, and now you lost control of your quirk!
Deku: W-what!?
Deku lended on the ground and noticed his shoot-style wasn't working, he was now a quirkless brat once more!
Villain: I hate to say this, but the effect of your quirk loss lasts for 1 or 2 hours, the time we need to destroy you!
Deku: D-Dammit!
The two Nomus appeared and one of them grabbed Midoriya by the neck, choking him in the air.
Toga: Hey! Hey! Let me have some fun with him!
Villain: Umm, sure…
The Nomu held Midoriya's arms and legs, immobilizing him, and putting him in front of Toga.
Toga: Have you ever kissed a girl, Deku?
Deku: Why would I tell you?!
Toga: Guess not, hehe. Can I be the first one, pleaaase?
Deku: No! Why would I ever kiss a villain!?
Todoroki: Midoriya!
A quick flash of flames launched by Shoto forced the Nomu to release Deku.
Toga: Oh c'mon! I was so clooooose!
Toga disappeared again.
Ochako: Deku, are you all right!?
Deku: Ochako, please tell me you're not Toga!
Ochako: Huh? What are you talking about?
Deku: What a relief! It seems that Toga has the ability to transform into other people, just like that girl Camie!
Todoroki: This is bad.
Bakugou (landed quickly): wow, no shit, Todoroki, it seems that Deku has nowhere to hide now and we are surrounded!
Deku: Where are the others?
Ochako: They are fighting the other villains, and it seems that Shigaraki is here too!
Todoroki: Shigaraki is dangerous.
Bakugou: wow no shi-
Deku: Everyone watch out!
The group of heroes quickly evaded the beam that almost hit them all, it seemed that one of the Nomu is now able to launch beams from its mouth.
In a matter of seconds, Eraserhead erased the Nomu's quirk and it stopped to launch beams.
Aizawa: Midoriya, since you canot use your quirk, you are incapacitated of fighting, you must escape the camp.
Deku: No! I can't do that! It's because of me this attack continues, if I leave, they will simply chase me!
Denki: Hey guys! I think we need your help in here! Me and Kirishima can't handle them all by ourselves!
Bakugou: I'll go help him, and Deku, watch your surroundings, I don't want you dead, you got it, nerd?
Deku: U-uh.. s-sure…
BOOM
A Nomu grabbed Eraserhead in an instant and threw him into the trees, breaking down logs and Aizawa's bones.
Deku: AIZAWA!
Todoroki: Midoriya watch out!
Todoroki quickly froze the Nomu, but it was useless, the Nomu just broke the ice and grabbed Shoto, throwing him into a rock and leaving him unconscious.
Deku: Todoroki, No!
Ochako: Deku! We need to run!
Both started to run, Midoriya couldn't use his quirk, and this made the situation even worse…
Bakugou: Wow no shit author
Katsuki, please don't make 4th wall breaks here.
…and all they could do was run, however, in an instant, a Nomu jumped extremely fast in Midoriya's direction.
Ochako: DEKUUUU!
The Nomu opened its mouth and launched the beam.
Deku was dead.
Ochako: N-NO! DEKU!
Uraraka couldn't believe he was dead, all was left in the ground was a crater, his body was completely disintegrated.
But… The Nomu looked behind itself, like there was someone behind him… it was impossible, Deku was there, standing backwards, he dodged the hit! But something was oddly different in him.
Ochako: D-Deku! Run! Why are you there standing?
Deku (thinking): All my friends are being defeated, Bakugou and the others can't handle it anymore, what am I doing? I should fight. I need to fight! But what is this sensation I'm feeling, I feel a need, a need to fight, what type of instinct is this? I don't feel any adrenaline. And yet, I still have this sensation… just what is this?
The Nomu jumped once more, and prepared its giant fist to smash Midoriya, and then, he simply dodged, with his eyes closed, and kept walking, like the Nomu wasn't even there. He was different, completely different.
The dodge was so fast that even Ochako's eyes just saw a blur teleporting himself behind the Nomu.
Ochako: Deku? Is that… really you?
Deku opened his eyes and turned his eyes to the Nomu, revealing such an odd glow, it seems that when he lost control over his quirk, he didn't get weaker, the loss of control he had earlier broke his past limits, revealing a power laid dormant in him for years, it wasn't a quirk, it was something even stronger.
The glow called the attention of the other villains, who looked to Deku, who looked calm and open for an attack, it seems that now, he really will be tagged.
Deku had achieved Ultra Instinct
Bakugou: Wow no shit author
Me: NO 4TH BREAKS, PLEASE!
The other Nomu jumped behind Deku, and he didn't even bat an eye, he just turned himself looking to any other side with his eyes closed looking even more open for an attack.
Meanwhile, on the other battlefield.
Bakugou: DIEEEEE!
Bakugou blew up another villain, and Kirishima alongside him, was using himself as a human shield, Denki was already in his retarded state, saying stupid stuff. Tsuyu was helping the others recover and Mineta was running like an idiot, Shoji and Ojiro were smashing villains on the way, but something called the attention of all class 1-A and the League of Villains, a mysterious glow in the forest, Bakugou, who was the closest to the location couldn't believe what he was seeing. Deku was dodging all the Nomus' attacks without any problems, he was dodging calmly and fast, it was impossible, they couldn't hit him!
Bakugou: What the hell happened to you, Deku?
Deku grabbed the two Nomu and threw it away like it was just trash, and quickly looked in a mountain, which Shigaraki was there, he somehow managed to locate him and the League of Villains members.
Twice: Shigaraki! What should we do? He is looking towards us!
Shigaraki: We wait. All of that was just a fluke.
Sako: I hope it's just a fluke.
Dabi: That glow is really interesting.
Toga: I don't know what happened to you Deku, but you are still cute!
Spinner: So we wait?
Shigaraki: Indeed.
The Nomu retreated to Shigaraki and kept standing there like body guards. And Deku didn't move a muscle, he just kept looking into Shigaraki is eyes, which were beind the hand in his face.
Kirishima: Is that… Midoriya?
Denki: Eh?
Todoroki slowly lifted himself, he could barely get up, but fortunately, he was able to get up.
Todoroki: Midoriya seems different than before.
Bakugou: Wow no sh-
Deku jumped towards Shigaraki, it took seconds to everyone to notice that Deku knocked a Nomu far away, and that he was already standing next to the whole League, looking extremely calm.
Spinner: This can't be a fluke!
Dabi: Twice, get him.
Twice: With pleasure!
Twice lifted his sword-alike measuring tape to cut Deku, jumping towards him. On the other hand, Deku was keeping his eyes on the Nomu, not giving a shit about Twice.
Twice: He's completely open!
Twice landed and slashed his tape through Midoriya, but he turned down extremely quick and dodged Twice's move.
Deku lifted himself and opened his eyes, which were with a tone of gray, now it was cleared. Something clearly happened to Izuku.
Twice: Hey! Don't ignore me!
Deku didn't say a word, all he did was break the cliff, making all the league fall down to the forest, calling the attention of the other heroes and villains, who were so stunned seeing Midoriya's new power that they only could watch.
On the forest, Todoroki was holding Eraserhead, who was extremely injured.
Aizawa: The pros should have been notified by now, I'm sure they are on their way.
Todoroki: It seems that Midoriya is facing down all of them at once. What a surprise.
Aizawa: Midoriya? All by himself?
Todoroki: Indeed. Something happened to him, and now he has gotten really powerful.
Ochako: Guys! I'm so glad I found you!
Todoroki: Uraraka, how are the others?
Ochako: They're okay, but, what happened to Midoriya? That's… not him at all…
Aizawa: I can honestly say one thing, those dodges are surreal.
The fight in the forest continued, Deku was dodging everything, they couldn't get a hit, Dabi's blue flames were completely useless, all Deku did was just walk away from them like it was no big deal, Mr. Compress awas also useless, if he can't touch him, Deku will never get caught. Young Midoriya was now almost invincible.
Meanwhile, on the other battlefield, Bakugou was watching Deku, he could only get angrier, his first theory about Deku was true, he WAS hiding a power in their entire life, he just couldn't use it.
Bakugou: Dammit Deku, why were you able to achieve this again only now? I remember that day, that kept worrying me about you being quirkless or not… these movements, they are so similar…
6 years ago…
Bakugou: Dammit Deku! Just throw the goddamn ball! You are wasting our time!
It was a sunny day at school and the students were playing dodgeball on P.E. class, Midoriya was the last one standing on his team, the others were already eliminated. The team Bakugou was in wasted all of his balls trying to hit Midoriya, who escaped them out of dumb luck.
Bakugou: WHAT ARE YOU WAITING FOR!? GO!
Midoriya: Uhh… ok…!
Midoriya threw the ball, but it missed and hit the ground, Bakugou quickly got the ball before any of his teammates and threw it at Deku with all he got, he was probably going to get badly hurt if that ball hits him.
But suddenly, Deku turned down and dodged the ball really fast, Bakugou's teammates couldn't believe what they saw.
Bakugou: Tch! This was just a fluke! But a fluke can't happen twice!
Deku grabbed another ball and threw in one of his teammates, the ball was so fast and precise that almost broke the nose of one of them.
Bakugou: W-what?!
Katsuki quickly looked into Deku's eyes, which were with a tone of grey and he looked serious, something definitely happened to him. All of them were certain that Deku was quirkless, but that thing made them doubt it.
Bakugou grabbed the previous ball and threw at Deku using his quirk.
Bakugou: DIEEE!
Bakugou exploded his hands making the ball fly towards Deku with an absolute strength, it could break his face!
The ball hit Deku and knocked him out, he was unconscious.
Bakugou ran into Deku's unconscious body and opened his eyes, they weren't grey anymore like he saw earlier, maybe he was seeing things.
*End of flashback*
Bakugou: It can only be… it…. But why now?
Midoriya had already defeated Twice and Spinner easily, they were both unconscious, now only Toga, Dabi, Compress and Shigaraki were left. The League of Villains was in clear disadvantage.
Shigaraki: This really can't be a fluke.
Bakugou: Dammit Deku!
Katsuki Immediately landed next to Deku,the other battlefield was clear, now all they had to do was wait until the arrival of the pros. But Deku was aiming for something else, he could only focus on defeating the League once and for all.
Bakugou: Tell me! What happened to you Deku?!
MIdoriya didn't even respond
Bakugou: Huh?! Are you ignoring me?!
The League soon realized Midoriya's classmates also didn't knew about his "fluke", it was something new and different.
Deku jumped, his amazing speed made him get to one of the Nomu and preparing a Smash, he broke the Nomu's face so badly that its body exploded into pieces and when he would prepare to jump to Shigaraki, the glow… disappeared.
Deku: H-huh?
Bakugou: What are you waiting for, Deku, kill him!
Deku: What.. just happened…?
Bakugou: Dammit…!
In seconds the League of villains retreated and escaped, the Pro heroes took care of the rest of the criminals and 1-A students' wounds and injuries, the attack was over, it was a relief.
Soon they were all back to U.A. in their dorms, all of Deku's friends were questioning themselves about Deku's mysterious glow back in the camp, but they didn't want to disturb Midoriya, who was writing down everything in his notebook, but at least, it was a new notebook about that weird sensation he got in the camp, the classes would be canceled for 3 days so they were free during that period of time.
Deku left his room and walked to the sofa looking exhausted, when he would sit in the sofa he heard.
Kirishima: Shoot!
All the boys started to shoot water balloons at Deku, he got all wet.
Denki: Aw, c'mon Midoriya! Do those amazing dodges you did back in the camp against the Villains!
Kirishima: Yeah! We wanted to see how you would dodge water balloons!
Deku: U-uh…
Aizawa: What are you doing?! Clean this mess now!
Kirishima/Midoriya/Denki: Yessir!
The mess was cleaned at least, but the investigation wasn't, all of Midoriya's classmates were curious about the way he fought against those villains and they wanted to activate that glow again.
The saga continues…
After the mess, the entire class 1-A got permission to train in Gym Gamma in these canceled class days, Midoriya thought it was going to be some regular training, but his friends had other plans.
Iida: Since everyone is here we'll start our chosen exercise
Deku: Chosen exercise?
Iida: Indeed, we noticed the villains were tagging you and you achieved that glow in the middle of the fight, we decided to make a special training just for you!
Deku: W-what? Really? Thanks then!
Iida: Glad you're grateful! Because we decided that the exercise will be combat training, and we will be all tagging you! In other words, you vs. everyone!
Deku: WAIT WHAT?!
Bakugou: You heard it right nerd, it's you against us all.
Kirishima: Since we saw you couldn't achieve that glow on your own, maybe it will go back eventually if we push it during the fight!
Deku: B-b-b-but I still haven't mastered it! How come I push it during the fight, and in fact, I will lose badly against you all! Is this a punishment…?
Bakugou: How about you master this ability now, huh?
Iida: Ok everyone, on your marks!
All the students surrounded Midoriya, who was almost freaking out, he wasn't Mirio to take down all 1-A at once, but he could at least try.
Iida: Ready… set…
Bakugou: DIEEEE!
Bakugou didn't wait and used his explosions to fast forward into Deku, who activated his shoot-style and used an air-pressure kick to stop Bakugou.
Iida: Don't ruin the plan Bakugou!
Bakugou: Fuck the plan!
Kirishima ran into Deku, giving consecutive hits into him, which Midoriya had difficulty evading all of his moves and then, jumped to evade the attacks, but was caught in Mid-air by Bakugou and was sent flying by an explosion.
Bakugou: What's wrong, Deku?! Why won't you fight!?
Deku: Full-Cowl 8%!
When landing, Deku gave a speed impulse that fasted forward him into Kirishima, evading Bakugou and smashing Kirishima into the ground.
Iida: Recipro… Burst!
Iida ran fast into Midoriya, pushing him against the wall.
Iida: Denki, now!
Denki launched a lighting of electrification to Midoriya, electrifying him and paralyzing him for short period of time, right after, Ochako Uraraka appeared and touched Midoriya, making him float to the air.
Ochako: Sorry Deku!
Iida: Todoroki now!
Shouto: No.
Iida: Why not?
Shouto: He is already paralyzed and I think that's enough for him, we can't force that thing out of him, we don't even know what that glow is or how it works, if we keep this up, he might die or something. Or get his hands crushed… I don't know…
Iida: You're right, hurting him won't do any progress, we should-
Bakugou: DIEEE!
Bakugou went straight to where Deku was floating and blew up him up, leaving him unconscious.
Ochako: Release!
Ochako released him softly into the ground so he didn't get hurt, he was really injured.
The others were complaining to Bakugou due to his disrespect against the plan, but he didn't give a fuck.
Mineta: Hey guys… wasn't Midoriya unconscious just now?
Denki: Yeah, why?
Mineta: Look…!
Deku was standing once more with his eyes closed, it almost looked like he was sleepwalking, but he looked oddly different, calm and open for an attack.
Denki: Hey guys! Midoriya is ready for more!
Ochako: But he is extremely injured!
Kirishima: But it doesn't look like he can't fight… somehow…
Bakugou: DIEEE!
Bakugou used his explosions to move forward to hit Deku, who was completely open for an attack, and then, he started walking towards Bakugou with his eyes closed.
Bakugou: What's wrong, Deku?! Giving up already?!
When Bakugou reached Deku, he suddenly dodged and continued walking.
Bakugou: W-what?!
Deku walked towards everyone and stopped, he was once more open for an attack
Denki: Hey Midoriya! Catch!
Denki threw a ray of lighting at Deku, which somehow went threw him like he was using Mirio's penetration quirk, but to the ones who looked carefully, Deku dodged the lighting so fast, that it was almost impossible to see with just bare eyes.
Denki: Eh? How did you-
Kirishima: It's that power again!
Iida: Indeed! We pushed it out of him!
Kirishima: And now..? What do we do? Continue fighting? I'm tired already!
Mineta: Yeah! We accomplished our goal! Make Midoriya activate that power! Let's get back to our rooms!
Aizawa: Hold on, Mineta.
Denki: Aizawa? What are you doing here?
Aizawa: It seems that we were able to restore the canceled classes, so you're all going to have lessons with me.
Everyone seemed to be extremely disappointed. But the glow in Deku's body didn't deactivate, he was still in Ultra Instinct.
Midoriya watched the classes in that form, which was distracting to the other students, who were almost intimidated to see a serious face and grey eyes, which were really scary to look at.
After class, the students would return to the camp once more, but now it was being protected so a villain attack won't occur again, at least.
Ochako: Deku!
Deku didn't even look at her.
Ochako: Deku, what are you planning to do after class?
Deku: I don't know.
The answer was almost rude, he was different after all, the state he was in left him completely calm, he didn't even blushed due to Uraraka being centimeters close to his face.
Ochako: You're really different! But where are you looking at? Are you even hearing me?
It almost seemed Deku was daydreaming.
Soon all students improved their quirks, Deku was looking at his hand, trying to figure out more about his power. He picked his recently bought notebook and starting down his sensation and feeling, but this time he wasn't muttering.
Soon the camp training was over, they didn't stay there for long, and Midoriya's glow wasn't over yet, in fact, it was growing stronger.
Meanwhile, in a high-security prison…
All-For-One: How boring… when will All-Might come here to talk to me again?
No one responded.
All-For-One was stuck in his cell; waiting for the perfect time to attack and escape, in fact, the League of Villains had a plan to get him out of his cell.
Twice made several clones of Toga that killed many policemen secretly and took their blood, transforming into them and taking control over the area, they were going to save All-For-One!
Soon, all cops were replaced by cloned Togas, and then a cop got into All-For-One's cell
All-For-One will be shortened as "AFO"
AFO: Who's there?
A bunch of slime slide down from the body of the cop, revealing the naked body of Toga Himiko.
Toga: It's me Toga! Let's get you out of here!
AFO: It's about time.
Toga released All-For-One and activated a lot of alarms, alerting the pro heroes.
All-For-One destroyed the entire cell, and almost the entire prison, killing all clone Togas and the remaining cops
AFO: All-Might, without you, the world is nothing! And I'll aim for your successor, All-Might! Because I know you exist, One-for-all successor!
These were the words class 1-A saw on TV, they were all frightened and scared, except for Midoriya, but he wasn't scared because he was in a different state.
Bakugou: Deku, come with me, now. In particular of course.
Deku walked with Bakugou to a distant place, they both knew the villains would tell All-For-One about Izuku's talks with All-Might, and that it would be obvious that Deku is the One-For-All successor; the next attack could be anytime now.
All-Might: I know what you're thinking already. They should know by now, and young Midoriya, that new state of yours is something completely new, you still can't fight All-For-One.
Bakugou: So what are we supposed to do? Stay here like complete retards? The symbol of evil is out there and we are all in danger! If you can't fight him, then who can!?
All-Might was speechless
BOOM
An attack happened, and now, it was in front of U.A.
Bakugou: THEY ARE ALREADY HERE?!
Everyone gathered around the room, this time, there was no one who could defeat All-For-One.
Shoto: This is bad
Bakugou: Wow no shit Todoroki.
*I'll stop the "no shit Todoroki" joke.*
Mineta: WHAT ARE WE SUPPOSE TO DO?! WE'RE ALL DOOMED!
Another explosion happened at the entrance, an there was All-For-One and a bunch of strong villains, and even worse, All-For-One was holding Endeavor, who looked really injured and incapable of fighting.
Shouto: He already defeated my father?!
Mineta: I TOLD YOU! WE'RE DOOMED!
Deku took a step forward.
Ochako: Deku? What are you doing?
Bakugou: Deku… don't tell me you are going to fight him on your own…
All-Might: young Midoriya, no! This is too dangerous for you!
Deku didn't respond any of them; he used a speed boost and reached the entrance where All-For-One was.
AFO: If no hero shows up, I think I'll have to destroy the entire U.A. at once!
Deku: Is it me you're looking for?
AFO: A student? All-Might sure has the weirdest choices for a successor, but I admire the courage of showing up, Izuku Midoriya.
Bakugou: Shit! He already knows his name!
All-Might: It must be that pussycat's quirk he stole!
Deku: I am going to send you back to prison once more, All-For-One.
AFO: Interesting how you're speaking calmly at a time like this, but I know all of your weak points. Your chance of winning is a maximum of 1%
Deku: There's still a chance then.
AFO: Why are heroes always like this? Stubborn and always hopeful they will win, but in the end, it's all the same thing…
Deku: Can we fight now?
AFO: Son of a… YES!
All-For-One warped many Nomus into Deku, all of them attacking him at once, when they finally reached him, he gave consecutive punches that stopped many Nomus, but soon they surrounded Midoriya and seized him into the ground.
AFO: How disappointing, already defeated, Midoriya?
All-For-One looked behind him, he clearly took time to notice Deku somehow dodged the attack and was standing on a destroyed pillar from U.A. That was so fast even All-For-One's enhanced senses and Search quirk took time to notice him.
AFO: Interesting… this doesn't seem like One-for-all.
All-For-One used Springlike limbs to power up his arms and throw an Air Canon beam at Midoriya, who jumped calmly to dodge the attack.
AFO: You can't dodge in mid-air!
All-For-One threw another Air Canon beam at Deku, but he succeeded in dodging in mid-air.
AFO: Something isn't right, huh? What you are using now isn't a quirk, but something humanity still hasn't seen… I must steal it.
In a matter of seconds, All-For-One speed up behind Midoriya grabbing him with his forcible quirk activation, this time, he didn't dodge.
AFO: But perhaps, I can have a little fun first before stealing it. You still can't control One-For-All completely , can you? Which means I'll break your bones first!
All-For-One started to force Full-Cowl out of Midoriya, it grown to 30%, making poor Deku's flesh to hurt insanely.
But suddenly, the glow in his body started to grow stronger; it seemed All-For-One made a terrible mistake forcing a power from his body, because the glow was shining so strong, an impulse of energy made All-For-One fly meters away.
The glow was so shiny, it was impossible to see Midoriya's body, only a white glow shining in the air.
AFO: What…?!
The glow lowered a bit, making it possible to see Midoriya. With a white aura and gray hair, he achieved, once more, a new level.
Deku: All-for-one, I'll send you back to prision!
AFO: You are a formidable foe, young Midoriya.
Meanwhile, inside U.A.
Bakugou: Dammit Deku, once more, what happened to you…?
Mineta: WHY IS HIS HAIR GRAY? DAMMIT MIDORIYA, YOU ARE ALWAYS TRYING TO SHOW OFF, HUH?!
Shouto: He got even stronger, somehow. That glowing aura seems to grow more and more when he uses it, and it seems that it reached its peak.
Ochako: Huh? What do you mean by that?
Iida: It's seems that power grew to some state that reaches a limit, it couldn't grow forever, and since All-For-One forced the glow out of him, it would reach its final limit.
Ochako: Oh I see! I was reading Deku's new notebook earlier, and it also talked about some limit. He named it after "Ultra Instinct" for some reason, I don't know why…
Denki: Wait, did you invade Midoriya's bedroom for that notebook? He didn't even left the notebook out of his hands.
Uraraka blushed
Ochako: W-WHAT?! N-no! Of course not! Who would invade someone's bedroom for a notebook!
Mineta: Of course... ( ͡° ͜ʖ ͡°)
*Back into the main battlefield*
Deku successively smashed All-For-One's face, sending him miles away, with this new form; he was now able to manipulate more than 100% of One-for-All easily.
AFO: I-impossible! How can such strength exist?!
Deku boosted behind All-For-One and kicked his back, once more sending him miles away.
All-for-one sent another Air canon into Midoriya in mid-air, but was easily dodged and counter-attacked by an air pressure strike made by Deku's leg, which smashed All-For-One.
Deku: I'll tell you again, I'll send you back to prision, All-For-One!
Shigaraki: No you'll not, Izuku Midoriya!
AFO: Shigaraki, no!
Shigaraki landed behind him to attack, but Midoriya was quick and fisted him in the face, sending him hardly into the ground, making him go unconscious.
Deku started to huff and All-For-One quickly noticed that Midoriya was somehow getting tired, his form was too much for him to handle for such long time, even at its mastered state.
AFO: So you still can't even handle that form either? You aren't as formidable as I thought, young Midoriya.
Deku *Thinking*: Dammit, if I keep up like this, The glow will disappear again! The next hit needs to do it! I'll have to break my arm!
Deku started to run towards All-For-One with an immense speed, charging his left arm with immense power.
Deku: One-For-All, 1 000 000%...
AFO: Come, young Midoriya! And meet your doom!
Deku: Delaware Detroit…
Midoriya boosted in front of All-For-One, and the villain warped a hostage in front of the hero, but in milliseconds, he speed up behind All-For-One, aiming for All-For-One's column and giving his ultimate smash upwards.
Deku: SMASH!
The energy wave was so strong, it almost disintegrated All-For-One, who was barely alive due to the power boost Midoriya received from Ultra Instinct. And in milliseconds, he speed up and grabbed the hostage, who was almost hit by the powerful blow. Giving a safe landing to the hostage.
Deku: My arm… didn't break…!
But Deku's happiness didn't last, his body started to release black electricity and a lot of pain, making he scream with a pain he had never felt.
Deku: G-GYAAAAHHH
Poor Midoriya fell on his knees due to such pain, his gray hair went back to the previous green/black hair he had before, and then, he fainted.
Midoriya woke up.
Deku: U-uh… where am I?
Izuku noticed he was in a hospital bed at Recovery girl's office.
Recovery girl: Impressive young Midoriya, this time you didn't break any bone and didn't need any healing!
Deku: W-whoa! Really!? How are the others?
Recovery girl: They are all alright and worried about you and something about a "glow".
All-Might: Young Midoriya!
Deku: All-Might!
All-Might: We have great news! All-For-One was sent back to prision by your own efforts, I didn't know you would have the potential to defeat him so early…! If he ever escapes again, you'll be able to defeat him once more, right?!
Deku: U-uh actually… I thing that glow's gone, for real now.
All-Might: Huh?
Deku: The power I used can't be achieved again, I can feel it's gone, I abused of it too much, and there's no way I will ever use it again. This means I'll have to return to my previous training schedule.
Young Midoriya explained the situation to his friends, who seemed really disappointed.
Kirishima: Bro, you defeated All-For-One with that! How come you can't use it again!?
Denki: Throw the water balloons at him and see if it's really gone!
Bakugou: That's a horrible idea, and Deku, now that you lost that power, I'll surpass you and become number one! You'll see!
Denki: Does that mean you were weaker than him all the time?
Bakugou: OF COURSE NOT! I NEVER SAID THAT, SCUM!
Everyone started to laugh, after the incident, they returned to their normal training schedules and classes, but Ultra Instinct wasn't forgotten and his classmates kept trying to push it out of him, poor Midoriya will never activate it again… the end…?