Last time on Dragon Ba- I mean The USJ Incident, the berserk Izuku has thrown Bakugou, his childhood friend/bully/frenemy into the walls of the USJ, All Might see that one of his students were hurt rushes in and tries to attack Izuku, Izuku reacts by doing the same, rushing towards All Might, and so the battle of the titans begins.
*for aesthetics*
All Might = AM
In the students' perspective, they see AM and Izuku teleport to each other leaving a colored trail behind All Might, and a black trail for Izuku. The students seeing All Might fighting gets them pumped up and cheers for him. Izuku sneers at the cheering but turns his focus back to the speeding AM, Izuku was able to attack first because of his superior speed and hits AM's face, AM then counters Izuku with a punch to the stomach, both fly off in opposite directions, Izuku flying a bit farther than AM bc he isn't as heavy, but Izuku sees a pole and uses the momentum of AM's punch and swings around flying back towards AM, AM just standing up sees Izuku trying to punch him puts up his arms in and X-formation and blocks the attack but his arms get some cuts and bleed a bit, AM counters by using Carolina Smash and the wind pressure pushes back Izuku enough for AM to jump back and charge a punch.
AM: Detroit Smash!
Izuku picking up a little bit of rebar from the ground: *smirk* You fell for it fool,(Thundercrossu Splito Attack) Full Counter
The shockwave of AM's punch gets redirected back at AM and makes a dent in his stomach, AM has a shocked expression then steps back and spits out some blood, he puts one of his hands to his stomach and one of his hands towards his lips and feels the blood, without any time for AM to react, Izuku punched him in the face, then in the stomach, hits his the other side of his face, then uppercuts him, then pummels AM's stomach making him spit out even more blood, finally kicking him in the knees and putting his foot on his head.
Izuku: Hah, so this is your number one hero? How pathetic. What are you going to do now? Your strongest hero has been obliterated. No one here has power that can compare to him, you're all weak.
Iida: Even though on our own we're not as powerful as AM, but we can work together as a class.
Izuku: Working together? Hah, don't make me laugh. You got rip-off spider-man, a person that can't completely control gravity, a weaker version of Ingenium, a male Snow White, Mr. Katy Perry Hot N' Cold, over there, a person who gets power from diabetes, edgy emo teen with a shadow, a pomeranian...
While Izuku was trash-talking 1-A, Bakugou has woken up from being unconscious, he rubs his head and sits up, what he sees shocks him, he sees "Deku" standing above AM. Seeing Deku being so strong angers him, even though he hates Deku, the reason for him trying to stop Deku was because he can't stand to see AM getting beat up, a hero who trained him for 10 months, he kinda went through some character development, but not enough to stop being a dick against Deku. Outside of Bakugou's inner monologue, a lot of the students and heroes were on one knee, harboring hatred towards Izuku's trash-talk and thus, not able to move or do anything.
Izuku: Hahahaha, hating me because of some trash-talk, how useless. Me just talking has already brought you all on your-
Bakugo: I'll fucking kill you bitch!
Izuku turns his head to the left and sees Bakugo flying towards him moving both of his hands forward, Izuku knew that that means Bakugo would make a large explosion. Izuku puts an Ark barrier to the side Bakugo is coming from and puts his left arm up in an L-shape and his opening his right palm to seemingly push on the Ark barrier for support, Izuku gets hit by the explosion, not damaging him severely but pushing him off of AM.
AM: Thank you young Bakugo, I'll take it from here.
Bakugo: No, I'm going to beat the nerd. You're injured, if you go you'll get beaten worse, I'm also destined to be a better Number 1 hero than you, so if you can't beat him, I will!
AM reluctantly stands down because he is too tired to fight, he's emitting steam, so Cementoss creates a barrier around him so that the students don't know about his weaker form.
*stop the music*
*then play this one*
Izuku: Oh? You're approaching me? Instead of running away, you're coming, right to me? Even though your teacher, AM, told you not to fight me, like an exam student scrambling to finish the problems on an exam until the last moments before the chime?
Bakugo: I can't beat the shit out of you without getting closer.
Izuku: Oh ho! Then come as close as you like.
Bakugo igniting the sweat on his hands, his body temperature rising with every spark, his hair seems to have tiny lightning bolts shooting through it, the aura surrounding him increases slowly, reaching a point where people can see it faintly, his eyes glowing with an orange tint instead of his usual red eyes, the meter on the grenade gloves rises, the small beep that is heard when it is full echoes throughout the USJ, sweat drips from his forehead to his cheek slowly running down his face to the ground
at the same time, Izuku Midoriya, standing opposite to Bakugo completely still with only the markings on him moving around forming different shapes and swirls, the darkness on his arms, the tips of his hair getting a little bit darker by the second, the longer he is in that state the more of his sanity he loses, so if Bakugo isn't able to beat him now, Izuku might lose all sense of self and sanity and starts to rampage throughout the city fueled by the darkness that overtook him
right before the drop of sweat hits the ground, the sounds of a bomb exploding are sounded, wind and dust blow it back as Bakugo has fully ignited the sweat on his hands charging at Izuku unleashed the first attack of his assault.
Bakugo: Explosive roundhouse!
Explosive roundhouse: a move created by Katsuki Bakugo, Bakugo uses his quirk to boost himself up in front of his opponent/s then doing a roundhouse kick at the face causing damage to the lower jaws of his opponent/s.
Izuku tries swiping at Bakugou's legs but he accidentally went under Bakugou's roundhouse kick, Bakugo quickly changes directions and punts Izuku right. in the back causing him to fall face-first into the concrete floor. Izuku becomes a bit more erratic, this continues for some time, each time Izuku gets hit, he becomes more and more predictable letting Bakugo hit him even more. Slowly, Izuku starts to slow down, and finally, his legs give up and he kneels and conceives the battle falling to the ground limply.
Explanations on why Bakugo was able to beat Izuku but All Might wasn't.
All Might: All of All Might's attacks are very flashy, but they are also really easy to predict since he yells out something smash every time, and Izuku was able to exploit this fact and use Full Counter on All Might's most famous move, Detroit Smash, with All Might yelling Detroit Smash and him cocking back his fist, it is quite obvious on what attack he's going to do.
Bakugo: Even though Bakugo is rash and short-tempered, he possesses quite a bit of battle smarts, from the fight with Cider House, we can see him blowing up the ice wall made by Todoroki making shards that can cut and injure the villains, incapacitating them without causing major burns, he also swiftly dodging the streams of water/ice/cider from Cider House and working in tandem with Todoroki to defeat the villains in a short period of time. From the final fight with Nine, Izuku temporarily transfers OFA to Bakugo, and from the short amount of time we see Bakugo with OFA, and him fighting someone he doesn't have a vendetta against, he's extremely powerful and uses tactics to dodge attacks while hitting the opponent at the same time.
Anyway, back to the story
After waiting for a few seconds, the heroes start to walk over to the unconscious body of Izuku Midoriya, they see that the darkness is moving toward the middle of the body collecting into a single spot, the spot slowly shrinks and seeps into the skin. The police force and ambulances make it to the USJ taking the unconscious villains to jail, the hospital, or the morgue. The teachers of UA, bring All Might and Izuku back, and interrogate him about the transformation he did, and have Recovery Girl heal him. This was the anti-climatic ending to the USJ, most of the students weren't hurt and the villain attack was under control.