Unforeseen Simulation Joint:
The scene pans to Izuku Midoriya sitting on the roof of a massive domed ceiling enclosing the USJ facility. The facility is divided into multiple zones: the ocean, natural disasters, heavy rain and fires, open areas, and mountains. These zones are all artificially constructed to simulate rescue training for the next generations of heroes.
Bzzzz Bzzzz Bzzzz
Deku's mosquito-spy (built with Hisashi's tech) had uncovered the League's plan to kill All Might with a bioengineered monster.
Skrrrrrrt.
Deku cuts a human-shaped circle in the glass, dropping a rope, and sliding down elusively without notice of canon participants in the USJ attack.
"What can I do?" panicked Momo Yaorozu as Kaminari was out of the count, Jiro's quirk was effectively neutralized, and she ran out of energy. Deku swoops in, activating D4C, who blitzes at the villains, crushing all their throats in the blink of an eye. Momo saw the villains dead on the ground, not knowing who had done it, but thankful for their survival.
Ribbit Ribbit
"WE'RE GONNA FUCKING DIE! PLS TSUYU, LET ME DO IT THIS ONE TIME," screamed Minata, terrified as the villains in the water zone climbed up with malicious intent. Tsuyu retorted, "Ribbit, even in this situation, you're a perverted loser."
Crack
The sea is filled with blood, and as Tsuyu and Mineta open their eyes, they see blood where the villains resided, terrified of who did it. Tsuyu quickly grabbed Mineta, escaping the water zone, and recuperating with the others.
The scene pans to the man-child and his pet:
"Master, someone's killing the villains; they seem to appear simultaneously in several zones," said Kuroirgiri. "WHAT? Since when do heroes ki—," screamed Shigaraki before he heard "Unlucky, I'm not your traditional hero." Deku activates D4C, who attempts to punch Shigaraki, but Kurogiri immediately teleports Shigaraki out of harm's way.
*FWOOSH*
The Nomu darts into action, creating winds blowing back the teachers and students watching as Deku's D4C and the Nomu clash momentarily. Nomu's shock-absorbent fists crash down, but Deku parries each strike, making sure to put his martial arts skills to use. Deku attacks the Nomu's Brain crushing it, and he momentarily enters a state of bloodlust and feeds the brain to the Nomu.
SCREECH
"That's disgusting, you can regenerate even from that, huh. Fine, let's see how well you can handle a punch", stated Deku as he blocked an attack from Nomu, purposely allowing it to launch him far. Deku's eyes dilate as he darts at the Nomu with incredible speed, penetrating through it with D4C, as blood splatters everywhere. He then removes D4C's hand from the donut-shaped hole he made in the Nomu and quickly devises a plan.
"Before you can even regenerate, I'll exile you. Dimensional Exile," whispered Deku as he turned around and hit the Cruxification Pose.
BOOOOOOM.
All Might dashes through the doors of the USJ like a normal person, and Deku is gone. Shigaraki and Kurogiri already escaped, and the Nomu's head is gone clean while the rest of the body stands. Deku exiled the Nomu's brain to another dimension, effectively decapitating it. If Deku wanted, he could have exploded the Nomu by bringing a parallel version of it to the real world.
Only Nomu's mangled corpse remains, proof of a power even All Might struggles to understand. (Remember, the Nomu was not damaged after All Might knocked it into the sky, and it landed back into police custody)