After their Hero Agency Internships, the students come back to school to resume their ordinary lives. However, instead of regular classes, Shota Aizawa announces that Class 1-A will participate in an amicable training exercise alongside four heroes-in-training from a nearby Hero school, Isamu Academy High School.
The four students present themselves as Kashiko Sekigai, Dadan Tadan, Romero Fujimi, and finally the snakelike Habuko Mongoose. It turns out that Hakubo was one of Tsuyu Asui's close friends back in middle school, so they are both happy to meet again. And contrasting with this friendship, Romero instantly clashes with Katsuki Bakugo, and during the rest of the exercise they do not stop provoking and insulting each other, despite the insistence of their respective classmates to stop.
After the presentations, Shota orders the students to change into their costumes and go to the Ground Omega, which is where the exercise will take place. Once there, All Might appears, and between him and Shota he explains to the students the rules of the exercise: The special activity turns out to be a team Survival Training, a sort of Battle Royale where the twenty-four students will split into six groups of four. Each team will star at a predetermined position that the teachers have chosen. The basic goal is just being to outlast all the other teams. If you beat up someone from another team you must tie them with the given Capture Tape to count them as eliminated. The last team to survive wins.
After this, the teachers announces the teams, and after finishing Shota orders them to move to their respective star areas, telling the students that the exercise will begin without warning in five minutes.
The teams enter Ground Omega and run to their star areas. When Team A reaches its position, Izuku Midoriya talks with his teammates about the best strategy to follow. Izuku notices that the survival battle royale setup puts his team at a disadvantage. Since they don't have anyone in their team who can spot others teams and they would be easily detected if they move, they decide that the best option is to lay low.
Meanwhile, on top of a watchtower, All Might and Shota contemplates the Ground Omega. Five minutes after the exercise starts, All Might comments none of the teams has begun to move yet, and asks Eraser Head why he chooses such a boring activity for the visiting guest. Eraser Head replies that in this time of the year energy and tension are high in all Hero Courses, so it's important to teach the students about avoiding fights, patience and self-control. All Might admits that he certainly have a point there but at that moment, Katsuki's explosion is heard in a distance, causing All Might to remark that not everyone likes to stay put.
The first team that faces him is the Team E. Kyoka Jiro manages to detect Katsuki's position using his Earphone Jack on the ground, and she tells her teammates that he is alone. Minoru Mineta and Yuga Aoyama decide to take advantage of the situation and ambush him. Yuga fires from the distance his Navel Laser, but Katsuki jumps dodging the attack. Taking advantage of the fact that he is in the air, Minoru throws several of his balls at him, but Katsuki dodges them, propelling himself with his explosions.
Deducing that they know he is alone, Katsuki shoots a powerful explosion against the ground. The blast sound is heard across the ground, hurting Kyoka and rendering her unconscious. Minoru throws several balls at the same time as Yuga approaches Katsuki to shoot him another laser, but Katsuki uses an explosion to deflect Minoru's attack on Yuga, who is covered by the balls and falling on Denki Kaminari, who at the time was helping Kyoka, also being caught by the Minoru’s Quirk. Grape Juice approaches to check that his teammates have been neutralized, but Katsuki appears and easily defeats him, tying the entire Team E with the Capture Tape, eliminating them from the exercise.
With a team eliminated, Katsuki goes out to find another, meeting Team D. Fumikage Tokoyami attacks him with Dark Shadow but Katsuki rejects him with an explosion, reminding him that his Quirk is useless against him. When Tenya Iida decides to take care of him, Katsuki chooses to flee, being chased by the class representative. However, when turning in a tree, Tenya enters an area totally covered of Capture Tape. Tenya tries to stop but can't and falls into Katsuki's trap.
By the time Katsuki's teammates arrive at his position, Katsuki has already defeated the entire Team D and got them all tied up. Momo Yaoyorozu is surprised that Katsuki has already defeated eight people on his own, and Eijiro Kirishima is glad to have him as an ally. With two teams out of commission Katsuki begins to look for the Isamu team.
Meanwhile, high on a hill, Kashiko uses her ability to keep an eye on Team B. She immediately tells her team members that Katsuki’s team is looking for them. Romero orders Dadan to explode them, to which he replies that he does not like to fight, but when Kashiko warns they are getting closer and closer, Dadan gets scared and launch a barrage of flash-bang missiles at Team B position, covering the area with smoke.
The Isamu team goes to check to make sure they didn't seriously harm anybody. While looking for their bodies they find that Momo created a sheet large enough for the entire team to guard against the attack. Seeing them unharmed, Romero prepares to use his Quirk.
As Katsuki launches into the air for his next attack, Habuko uses her Quirk, which paralyzes Momo, Eijiro and Mezo Shoji. However, Katsuki had already jumped in the air before he could be stunned, so he becomes paralyzed while in midair. As he begins to fall Katsuki become able to move again. He laughs and mocks Mongoose that her Quirk is weak as it only last three seconds. Fed up with his mocks, Romero Fujimi explodes in rage and releases a bunch of pink gas, despite his teammate Kashiko warned him not to do it.
The gas completely covers the area, and expands to where defeated Team D and E are. Team A decide stay away from the strange pink mist. Meanwhile, on the top of the watchtower, All Might and Shota see the pink gas. Shota recalls reading in the Isami students' data sheets that Romero's Quirk is rather troublesome, and he think they should stop the exercise, but All Might stops him and tells him that's okay. The students are in a survival training after all. If things get bad he'll stop it.
While they going up a hill to get away from the gas, Team A encounter Team C. Izuku and Shoto Todoroki both note how this must be an ability of one of the Isamu's students and agree to a temporary truce. Then, they see their zombified teams B, D, E and F come out of the mist and begin to randomly attack anything in their path. Romero Fujimi comes out and proceeds to mock the remaining U.A. students, only for a zombified Katsuki to sneaks up behind Romero and bite him, infecting him with his own virus and turning him into a zombie.
The zombie students begin to climb the hill and approach them to bite them. Shoto tries to hold back them with his ice, but the virus makes them stronger so they break through Shoto's attack. Suddenly the survivors hear Mashirao Ojiro yelling behind them, and when they turn around they see that both he and Toru Hagakure have been bitten by Eijiro and Fumikage respectively, becoming zombies. Koji Koda was also bitten but nobody noticed because he is still as silent as ever.
Izuku tries to analyze the situation and realizes the zombies still resemble their former selves. Then, seeing the zombies approaching, they decide to flee down the hillside. Being worried about her friend Hakubo Mongoose, Tsuyu does not see a rock protruding from the ground and trips over, allowing a zombified Habuko Mongoose to catch up to her. However, she is able to remember Tsuyu and refuses to attack her, and Tsuyu happily realizes that her friend recognizes her even in her current state. This touching moment is ruined when a zombified Yuga comes up from behind Tsuyu and bites her, turned her into a zombie.
The survivors begin to be worried about the way the situation is taking, when they hear the laughter of All Might announcing his presence by bombastically leaping down from the sky. All Might comes to save the remaining students, but as he lands, he turns back into his weak form due to overusing his muscle form. Izuku is stunned because he thinks All Might's secret has been revealed but, in a way, fortunately Ochaco Uraraka and Mina Ashido believe that he is just some stranger who has become a zombie and run away, dragging Izuku along.
All Might tries to explain that he is not a zombie, but then, the real zombies creep up behind him. All Might curses realizing he's helpless and in the middle of them all, but instead of being bitten, he gets patted on the shoulder when the zombies mistaking his real form as one of their own and leaving him alone, much to All Might's dismay. And then, it occurs to him that he has no idea how to stop the zombies.
Izuku, Shoto, Ochaco and Mina manage to escape the horde and hole up in a cave. Shoto creates an ice wall to barricade themselves from the zombie. While they discuss what to do, the zombies begin to gnarl at the wall Izuku remarks its only a matter of time for them to breakthrough. Izuku decides that the best option is a frontal breakthrough, so, he unleashes a Full Cowl Smash, causing a burst of air that clears the way for his group to escape.
Unfortunately, the moment before the attacked was launched, the effects of Zombie Virus are reversed and the students are returned to normal, leaving Izuku to apologize to his now confused, injured and falling friends. Unaware of what really happened and holding an injured Romero, an enraged Katsuki sees Izuku’s previous smash as a challenge and declares that he must want to fight. Izuku tries to explain the situation, but Katsuki blows him up with a Howitzer Impact.
In the distance, Shota grumbles all the mess that this situation has caused.
With the training exercise concluded, everyone's injuries are patched up. The Isamu students bid farewell to 1-A and attempt to make Romero Fujimi apologize for his attack. Similarly, the U.A. students try to make Katsuki apologize for his violence. They then bid their farewell.
Meanwhile, an Izuku is at the hospital in a full body cast. All Might attempts to cheer him up by buying him some snacks but Izuku Midoriya can't eat because his mouth is wrapped due the injures.