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The U.S.J. Incident (事件) was a villain attack on Class 1-A at the U.S.J. orchestrated by the League of Villains in an attempt to kill All Might.

Prologue
After the news breaks that All Might is teaching at U.A. High School, the press crowds the entrance to the school in search of an interview from the ultra-popular pro-hero. Tomura hides behind the crowd and eventually destroys the school's defense system. This allows the media to get onto school grounds, forcing the alarms to sound and panic erupts among the students.

Tomura uses the opportunity and steals an itinerary for Class 1-A and discovers that All Might will be teaching alongside Thirteen and Eraser Head at an outside facility. The League of Villains gather dozens of petty villains in anticipation of a chance to kill All Might. The following day, Shota Aizawa takes Class 1-A to the U.S.J. for specialized rescue training with Thirteen. All Might overuse his power that morning so he doesn't attend the training.

Just before the training is set to begin, the League of Villains invades the U.S.J. using Kurogiri's Warp Gate Quirk.

Incident
The League of Villains invade in search of All Might, and are confused when they don't see him among the faculty protecting Class 1-A. Tomura plans to attack the students in order to draw out their target. None of these alarms sound off in the facility. Shoto Todoroki discerns that the villains are likely jamming the alarms and communications using one of their Quirks.Shota asks Thirteen to protect the students and head for the exit. He storms the U.S.J.'s central plaza and attacks the villains, quickly dispatching many of the lower level thugs. Kurogiri manages to slip by the Erasure Hero and confronts Thirteen and the students before they retreat. He asks them where All Might is and then Katsuki Bakugo and Eijiro Kirishima suddenly attack him. He evades their explosive assault and then uses his Quirk to warp the class and scatter them across the various regions of the U.S.J. facility.

The League of Villains planned to separate the students by warping them to the different zones of the facility where villains wait to ambush them. The villains are mostly unaware of the student's abilities and Kurogiri warps them at random. Izuku Midoriya, Tsuyu Asui, and Minoru Mineta are sent to the shipwreck zone. Shoto and Toru Hagakure are sent to the landslide zone. Denki Kaminari, Momo Yaoyorozu, and Kyoka Jiro are sent to the mountain zone. Fumikage Tokoyami and Koji Koda are sent to the windstorm zone. Mashirao Ojiro is sent to the fire zone. Katsuki and Eijiro are sent to the ruins zone. Thirteen and the remaining members of Class 1-A are left to deal with Kurogiri.Izuku, Minoru, and Tsuyu work together to fight their way out of the shipwreck zone. They plan on regrouping with Shota so they can support him at the central plaza. Shoto easily routs the villains near him by freezing them. He interrogates them and finds out their plan to kill All Might. Momo, Denki, and Kyoka survive an ambush from the villains by using Denki's Electrification Quirk to subdue them. As soon as they believe they've won, an electric-type villain appears and takes Denki hostage.

Tomura closely studies Eraser Head's moves against the other criminals until he decides to confront the hero himself. Tomura takes advantage of the lapse between Shota's erasures and destroys Shota's elbow using his Decay Quirk. Izuku, Tsuyu, and Minoru watch in horror as Tomura calls Nomu to crush Shota.Kurogiri turns Thirteen's Quirk on itself and routs the Rescue Hero. Tenya Ida follows Thirteen's last orders and attempts to escape from the U.S.J. in order to find reinforcements. Tenya makes for the exit and his peers support him. They're able to hold off the black mist villain long enough for Tenya to escape from the facility and run toward U.A. High. Katsuki and Eijiro overcome all the villains in the ruins zone. Eijiro wants to go save his peers but Katsuki believes that their classmates can handle themselves. He decides they should go after Kurogiri because he's the villains' escape route. Mashirao, Fumikage, and Koji also persevere in their respective battles.

Kurogiri informs Tomura that one of the students escaped. This angers Tomura and he admits it's game over if Pro-Heroes show up. Minoru overhears this and believes the villains are going to retreat. Tomura notices the triad and attacks them. Shota erases his Quirk in time to save Tsuyu and Izuku uses a full-powered smash on him. Nomu absorbs the impact, protecting Tomura from Izuku's attack. Izuku surmises that Nomu's defenses are likely how the villains plan to take on All Might. Just before Tomura and Nomu kill the three students, All Might arrives to save the day.

All Might swiftly save Shota and routs the remaining weaker criminals. Then he rescues Izuku and company and asks them to take Shota to safety. Despite being unable to see All Might move, Tomura claims that the symbol of peace is weakening. All Might attacks Tomura, but Nomu comes to his aid. All fights Nomu until Kurogiri traps him using a warp gate. Kurogiri attempts to crush All Might in the portal while Nomu holds him.

Izuku rushes back to the scene and Kurogiri attacks him. Katsuki saves Izuku, blasting Kurogiri and pinning him down after exposing his physical body. Shoto freezes Nomu, allowing All Might to get free from Kurogiri's trap. Eijiro attacks Tomura, but he easily evades. These four students stand by All Might in his struggle with the League of Villains. Tomura is impressed that the students managed to subdue Kurogiri and Nomu.

Nomu suddenly breaks free from Shoto's ice and regenerates his broken limbs. Then it attacks Katsuki in order to free Kurogiri. All Might saves Katsuki in time but ends up taking a direct hit from Nomu as a result. The boys wish to help All Might finish off the villains, but All Might tells them not to attack and takes Nomu on alone. Tomura plans to kill the students while Kurogiri and Nomu fight All Might. With all of his remaining power, All Might takes on Nomu alone.The shockwaves produced by their epic confrontation keeps Tomura and Kurogiri at bay. All Might tests the limits of Nomu's Shock Absorption Quirk by going beyond his own limitations. All Might manages to slam Nomu into the ground and break it beneath him as the students and villains watch in awe. As Nomu gets up, All Might charges up his finishing move and teaches Nomu the meaning of Plus Ultra by hitting it with a smash so powerful it sends Nomu through the roof of the facility.

All Might reaches his limit and tries to intimidate Tomura and Kurogiri into retreating. They don't take the bait and attack All Might. Izuku rushes to All Might's aid, but Tomura and Kurogiri counter with a team maneuver. The weaker villains start to recover and the electric-type villain threatens Denki's life. Izuku's face is nearly destroyed by Tomura, but Snipe shoots Tomura and saves him. Tenya returns to the U.S.J. with the U.A. teachers in tow. Snipe shoots Tomura several times and injures him, forcing Kurogiri to shield him. Ectoplasm and Present Mic quickly rout the other villains while Thirteen attempts to capture Tomura and Kurogiri using their Quirk. Thirteen nearly captures them, but Tomura and Kurogiri manage to warp away in time.

Aftermath
The teachers manage to subdue the remaining criminals and rescue the students from their respective zones. Everyone exits the building once things are secure. Tomura and Kurogiri manage to return to their hideout and Nomu is apprehended by the police. Detective Tsukauchi and the police debrief the students and confirm the status of everyone involved. He confirms Izuku, Shota, and Thirteen will all be okay. The students discuss their fights until they are dismissed and return to school.

Nezu, Midnight and Snipe decide it's best to overhaul the security system and ponder Kurogiri's unique Quirk. Later on, Naomasa visits All Might and Izuku in Recovery Girl's office. Naomasa praises the teachers for protecting the students. All Might responds by claiming the students fought just as hard. He says no group of first years has ever dealt with an attack like that so early in their training. All Might believes they will learn from this experience and become great heroes one day.