Izuku Midoriya vs. Tomura Shigaraki & All For One

Deku vs. "Tomura Shigaraki" is a battle taken place during the Final War between Deku and and the unstable fusion of Tomura Shigaraki and All For One.

Prologue
After finally arriving back at the floating U.A. from being initially thrown off course, Deku is sent into shock upon seeing the devastation left behind by "Tomura" and all his unconscious allies, in particular Katsuki Bakugo, causing his Quirks to erupt out of control due to his overwhelming emotions. "Tomura" tries to take advantage of his emotional state to attack him, but Lemillion is able to calm him down and bring him back to his senses. With everything back under control, Deku confronts "All For One", asking if Tomura is still in there.

"Tomura" simply responds that no one by that name exists anymore, claiming that both Tomura Shigaraki and All For One have achieved a perfect melding, and because the latter has been alive longer, he's the one currently in charge. He states he has no idea what the young hero is scheming, but he won't get his ideal ending. However, Lemillion retorts back at the Villain, referring to the incident shortly prior where he had made a comment about how he doesn't have any friends, and "Tomura" hysterically cried out, as if he was possessed by a child, adding that the more they fought him, the more unstable he got.

"Tomura" is visibly irritated by the response, when Deku and the visage of Nana Shimura notice on "Tomura's" blob of a left hand the faces of the Shimura family, including her son Kotaro. This confirms to the both of them that Tomura is still in there.

Battle
An enraged "Tomura" leaps into the air, with enough force to completely shift the balance of the U.A. Flying Fortress. He angrily declares he's done playing games, and he is taking back One For All as he unleashes a powerful punch directly at Deku, destroying most of the surrounding area. However, Deku managed to stop "Tomura's" by combining Fa Jin's stored up energy into Blackwhip to create a Blackchain that ensures around his arm. He states he won't let "All For One" have his ideal ending either, and proceeds to toss the Blackchain away, smacking "Tomura" into several separated pieces that broke off U.A.

Landing on one of these blocks, "Tomura" says the same trick won't twice, but is surprised when Deku undoes the Blackchain himself. He notices him standing on a block concentrating to himself, when the Second User appears before Deku, warning him that once he uses it he'll be done, so needs to take him down within five minutes. Deku activates the Second's Quirk, Gearshift, which allows him to adjust the speed and trajectory of anything he touches.

Using the Transmission technique, Deku utilizes Gearshift on himself, catching "Tomura" completely off guard as in an instant, Deku appears underneath him, adjusting himself between "Second", "Third", and "Top Gear", bombarding him with a barrage of super-fast and powerful punches. The force is so strong it sends "Tomura" flying into the air, coughing blood, while Lemillion, who is rescuing all the injured allies from the previous battle, notes how the punches are so fast the sounds are delayed.

"Tomura" is baffled by what he is doing, realizing the speed is different from the glowing energy of Fa Jin he had noticed earlier, and figuring out what Quirk it really is. The vestige then responds that the Quirk is a much different beast than it was back in their day, just as Deku activates Gearshift: Overdrive, combining the 100%-esque power he stored up with Fa Jin at incredibly blistering speeds, reaching a level of power equivalent to 120%. With this added boost, Deku unleashes a devastatingly strong Detroit Smash directly into "Tomura's" stomach, all as Yoichi addresses his brother that today is the day they end this.

Within Tomura, All For One recalls back to the time in the past when he confronted and killed the Second User, when Gearshift could only work on small objects and likened it to that of a peashooter, believing all they were meant to be was unruly insects in his way. "Tomura" now begins to notice the vestiges of One For All around Deku, wondering how he is able to see them now.

Before "Tomura" can recover after being smashed downward, Deku uses this new ultimate potential of Gearshift and unleashes Detroit Smash: Quintuple, releasing five consecutive Detroit Smashes in quick succession, barrelling himself around the arena. "Tomura" notices the attack was lighter than before, realizing he didn't have the Fa Jin glow built up for it, but even though he is too fast to see, he tries to use the trajectory of the attacks to know where he is going to hit him and counter.

"Tomura" swings, but misses, as Deku had switched Gearshift into "Low Gear", slowing him down, as the Quirk can adjust speed without abiding by the laws of inertia. "Tomura" tries once again with another attack, but Danger Sense alerts Deku and he releases a Smokescreen, distracting "Tomura" for long enough for him to use Float to get above him, and carry him into the air with Blackwhip. Explaining how he effectively used all the Quirks of the users, Deku further reveals the Quintuple Detroit Smash built up more energy for Fa Jin, allowing him to execute another Overdrive attack.

The Second User tells "Tomura" that their Meta Abilities were never what he should have been wary of, but rather the reason why someone chooses to use their gifts, and that true power resides in the indiviual's intent, which is why they are called "Quirks". Deku angrily declares he is giving it everything he's got and that All For One doesn't get to hurt anyone else. "Tomura" helpless spews more insults as Deku releases a powerful smash attack that completely destroys "Tomura's" finger defense form, and leaving him with a gaping hole in his chest.

Yoichi tells Deku that One For All and All For One are resonating with each other, just as Tomura and All For One can see the vestiges with Deku, they can see All For One's vestige struggling for control with Tomura. He continues that Lemillion was correct that the previous battle has shaken the balance of their intended melding, with the Second User responding that he can't take it easy yet, with Deku attempting to recover.

Continuing to fall, "Tomura" is further incensed, as he has been unable to use any of his Quirks at all, or the true value of his body, all because of Erasure, the U.A. coffin, and the Heroes' separation plan. But yet despite this, he refuses to give up as a massive lump begins to emerge from his chest as he screams in pain, all the while All For One declares that victory is still within his grasp.

Meanwhile outside U.A. on the observation deck, Phantom Thief continues to Copy Erasure to keep "Tomura's" Quirks shut off, assisted by Eraser Head and Manual. They start to have some trouble due to the sudden increase in winds and weather, as an unintended side effect of the intense heat being created by Endeavor, Shoto, and Dabi's battles. Despite this, Phantom Thief continues to keep his eyes open, knowing everyone is still fighting, and intent on being just as responsible for saving the day. However, an unexpected arrival throws everything off course.

Spinner had successfully freed Kurogiri from his containment at Central Hospital and began using his Warp Gates to reach his allies. What's more, on Okuto Island, Himiko Toga had successfully injected the vial of Twice's blood, allowing her to Transform into Twice. Kurogiri warped himself and Present Mic onto the observation deck, catching Eraser Head off guard, and before he can reach, Kurogiri opens another Warp Gate in which a swarm of Twice Doubles emerge and begin to attack. Eraser Head and Manual try to defend Phantom Thief, but they are immediately tossed to the side, and Phantom Thief is tackled to the ground, shutting his eyes, and undoing Erasure.

As a result, a screaming Tomura begins to emerge within the scab on his stomach, and with his Quirks returned, unleashes a massive explosion that destroys most of the U.A. Fortress. The students and staff within struggle to but are unable to keep up with most of the repairs, and things get into even more trouble when Mandalay reports in that they have been hacked, courtesy of Skeptic, and that U.A. is starting to fall toward the ground.

Deku recovers from the explosion to see Tomura standing there amongst the rubble, having shed most of his skin. He also sees Kurogiri appear right next to him, while also noticing Tomura's struggling to move. Just then, Tomura speaks to Deku asking what he would do if "he" was here now, sarcastically asking if he wants to chat at the mall, which isn't happening, since he is his villain. Deku realizes that Tomura's original persona has re-emerged.

Between the chaos of the falling U.A. and Kurogiri, Deku tries to think of a way to fix everything, but due to the blowback of using Gearshift, he's run out of air and found it harder for him to breathe. Despite this, the Second User notes out that All For One is unable to manipulate Tomura's flesh at the moment either, so the two are left to stare each other down and recover until one's body is able to act and make the first move.

Suddenly, U.A. is saved from falling by what is described as an "air trampoline", which Deku immediately recognizes who it is: Gentle. After proving himself worthy, the Police Force had agreed to let him assist them as a form of redemption, and while La Brava got to work in over-hacking Skeptic and fixing U.A.'s flight system, Gentle was sent onto the battlefield, using his Elasticity Quirk, empowered by La Brava's Love, to release Gently Super-Lover, stopping U.A. from its descent.

Daigoro Banjo warns Deku to be careful as Tomura manages to regain control of his body and is about to touch the ground to activate his Decay. But before he can, a sharp pink bullet comes out of nowhere and shoots Tomura's right hand right off, which Deku also recognizes as being thanks to Lady Nagant and her Rifle Quirk, who was able to snipe him from below in the city atop Central Hospital.

Using her last remaining strength, Nagant shoots off Tomura's left hand right when he tries to attack with the other, giving Deku just enough time to recover and regain his own strength. Within Tomura, All For One hysterically lambasts Nagant for her patheticness, only for Tomura's true self to begin re-emerging from the vestige, mocking his master's attempts at manipulation having failed.

Tomura reveals he had realized All For One's plans to manipulate him and use him as a vessel, so to combat this, he had kept his "origin" as "Tenko Shimura" hidden deep within All For One, building up its hatred under his nose until the opportunity to take back control came about. All For One tries to command Kurogiri to warp Tomura to his main body, but due to the persona of Oboro Shirakumo within him, Kurogiri malfunctions and is unable to properly respond.

Using a mass of fingers to completely break free from All For One's vestige, Tomura declares that he doesn't need One For All, and his intention to stay true to his original goal: to destroy everything in the world that created the house he grew up in, and that's the only thing that will save him. Knowing that Tomura has access to his Quirks now, Deku takes the opportunity to grab ahold of him and blast him directly outside U.A. onto the ground below. Tying his arms up with Blackwhip, Deku confronts his Villain, stating that while he can't let him do that, he also won't pretend he didn't see him crying before.

Aftermath
Unbeknownst to him or Tomura, the students from the Hero Business Course were recording their brutal battle from above U.A. Fortress, as Izuku disables his Blackwhip to charge right at Tomura in full speed, as the two continue their clash with Tomura gleefully laughing during it.