Izuku, along with his classmates, travel to their chosen workplaces to gain hero experience and training under the supervision of pro heroes. Meanwhile, evil begins moving about in Hosu, eventually leading to a confrontation between three young heroes and their first formidable villain.
Following the Sports Festival, the students are encouraged to get field experience by training under acting pros. After the class decides their hero names (except Bakugo), everyone is ready for their experience, though Bakugo and Todoroki received an overwhelming majority of the requests. Bakugo ends up going with the hero number 4 Best Jeanist, because he was the highest ranked hero to request him and Todoroki goes with his father in order to learn from him.
Midoriya ends up getting a single request to work under an old hero named Gran Torino, All Might's former teacher.
Ida acts oddly, after his brother has been crippled by the Hero Killer Stain, a mysterious villain that is taking down heroes he deems unworthy. He interns under a hero named Manual, but plans to find and kill the Hero Killer when he gets the chance.
As for the rest of the class: Kirishima and Tetsutetsu join Fourth Kind, a chivalrous public servant hero that keeps them in a tight leash. Yaoyorozu and Kendo join Uwabami, a hero with a side gig as model to which they are also made to participate. Uraraka joins Gunhead, a soft-spoken hero who teaches her hand to hand combat. Mineta works under Mt. lady, but is actually made a maid for her and does her everyday chores. Tsuyu takes part in the crew of the seal hero Selkie. Although this is not disclosed until later arcs, Tokoyami interns under the Number 3 hero, Hawks. Jiro interns under Death Arms.
During his training, Midoriya learns he can use his quirk better by spreading the energy through his entire body, instead of focusing his power on a single limb, which has been breaking his bones. With this new knowledge, he creates Full Cowl, a technique where he uses a small amount of One for All (initially 5%) to give him an overall boost in physical capability without the self-destructive consequences of using the Quirk's uninhibited power.
Meanwhile, the Hero killer Stain has been making headlines, and the League of Villains tries to recruit him, but is unsuccessful due to their difference in ideology: the Hero Killer is trying to cleanse the image of heroes to perfection, Shigaraki is trying to destroy heroes, though they agree they both want to tear down the current hero society. Elsewhere, Naomasa informs All Might that the Noumu he fought with used to be a normal human and an ex-con.
Tomura unleashes a horde of Noumus in the town, together with Stain going after the heroes. Midoriya and Gran Torino save the train they were taking. While heroes and Noumus fight, Midoriya figures out Ida's plan to find the Hero Killer and finds him almost killed as the Hero Killer tries to take another hero down.
Midoriya is able to use his new powers to fight a little before being paralyzed, but Todoroki comes there after receiving a message from Midoriya. The three are able fight back against the Hero Killer and get him down as reinforcements are coming. Midoriya is taken by a flying Noumu and Stain rushs to save him, having considered him a worthy hero.
When Endeavor gets to the scene, Stain is arrested and Midoriya, Ida and Todoroki are taken to the hospital, where they are told that even though they did something good, they broke the law and the story will be supressed, with the official version being that Endeavor took down the Hero Killer alone.
Ida asks for forgiveness to his friends, refusing a surgery to eliminate the scar in his arm to remember his bad decisions.
The period of field experience ends and Gran Torino has officially recognized Midoriya as a great successor to All Might.
Tropes
- Anti-Regeneration: Endeavor defeats a Nomu with a "Super Regeneration" Quirk by making his flames hot enough to turn blue and carbonize the head off.
- Arc Villain: Stain.
- Armor-Piercing Response: When Ida is consumed by vengeful rage and hunts down Stain for crippling his brother, he vows to exact retribution upon the Hero Killer. Stain's response? He points at the injured hero behind him and says:
- Stain: "Save that guy first."
- Bad Powers, Bad People: The Hero Killer paralyzes people by licking their blood, making him a terrifying villain.
- Brick Joke: During Kirishima and Tetsutetsu's match during the final round of the Sports Festival, the viewers made a remark how it would be great to have them both as sidekicks. Sure enough, here they become sidekicks of the same hero for their internships.
- Can't Get Away with Nuthin': Midoriya, Ida, and Todoroki get penalized for getting into an unlawful fight with a villain due to the strict rules modern society has developed to adapt to quirks.
- Chew-Out Fake-Out: Downplayed. Police Chief Tsuragamae reprimands the students who faced Stain when they were [legally] not allowed to, but goes off record in complimenting them for doing so as it is still the right thing to do.
- Contrived Coincidence: Iida, Midoriya, and Todoroki are all at close proximity with each other, thanks to the Nomu attack on the city, allowing Midoriya to find and save Iida, with Todoroki not far behind.
- Create Your Own Hero: All Might reveals that his and Deku's Quirk "One For All" was created by a villain who could give and take Quirks. The villain gave a Quirk to someone who already had one, which led to One For All's formation. The users of One For All all opposed the villain, and the villain was eventually defeated by All Might.
- Darker and Edgier: After the lighthearted Sports Festival arc, the story takes a darker turn when Shigaraki returns and Stain makes himself known.
- Defiant to the End: Though defeated and bound, Stain refuses to fall against the "fake Heroes", and his own determination stops everyone in their tracks. Thankfully, a serious injury from his fight finally stops him.
- Degraded Boss: This arc introduces more Nomu, but they're much weaker than the others and even the strongest is taken care of by Endeavor with relatively little fuss. It's explained that the original Nomu, being made to match All Might, was made stronger and had better Quirks, while the lower-tier ones here were made for quantity over quality.
- "Eureka!" Moment: Midroira discovers a way to properly handle One For All: instead of focusing on one limb or finger at a time, he should spread the power throughout his body, inspiring a new form of One For All called "Full Cowl".
- Evil Is Cool: Invoked and Deconstructed with Stain, the manga shows how damaging the concept can be to society, especially young people since the attention Stain gets from the media encourages already troubled people such as Himiko and Dabi to become full time villains. This is also troublesome because even if these villains are cool they are still evil, shown when Kaminari praised Stain's coolness, failing to realize he just praised the man who permanently crippled his classmate's brother right in front of said classmate (or was almost killed by the same man) until he is called out on it. Iida decides that Kaminari isn't wrong about Stain's cool factor because of his convictions, but refuses to excuse his actions.
- The Greatest Story Never Told: Deku, Todoroki and Ida survive Stain's onslaught and even rescue Mr. Native, but tales of their heroics can never be told since they committed a violation of performing superheroics without any license; If word got out, they would have to be punished. As a result, Endeavor would gain all of the credit from that night.
- Love Is a Weakness: Gran Torino points out Deku's idolization of All Might has warped his expectations of his hero and of the power of One For All, hindering his combat ability by making him think of his Quirk as merely a Special or even a Finishing Move.
- No Good Deed Goes Unpunished: Midoriya and Iida's mentors have their liecenses temporarily revoked after the students fought Stain.
- Only in It for the Money: This is one of the many examples of "corruption" Hero Killer Stain wanted to excise from the world of heroics, leaving only those in it for the sheer sake of heroism.
- O.O.C. Is Serious Business: Iida is usually a strict rule-abiding student of UA, but after learning his brother is injured to the point of retirement, he chooses Revenge Before Reason and goes after Stain, almost getting himself killed in the process.
- Shut Up, Hannibal!: Ida gives one to Stain when it looks like Stain is about to kill him. He doesn't care what Stain thinks of him or the heroes he's attacked. Stain is still just a criminal who hurt his brother. This is immediately followed by Deku rushing in and Smashing the Hero Killer in the face.
- The Only One Allowed to Defeat You: Stain declares that All Might is the only one "allowed" to kill him since he sees him more of a "true hero" than all of the "fakes".
- Time to Unlock More True Potential: This is what happens to Midoriya at the start of the arc, with the retired hero Gran Torino as his mentor.
- Villainous Rescue: Stain rescues Deku from a Nomu that tries to fly off with him.
- Villain Has a Point: While his method of dealing with "fake heroes" is more than extreme, Stain isn't entirely wrong in seeing how hero work is treated as more of a business or a pursuit of fame than a good deed. While All Might is no less a celebrity, he is considered a "true hero" by Stain because he treats his career exactly like that of a traditional hero and, thus, declared only he is allowed to defeat/kill the Hero Killer. He also criticizes and targets Iida because the student was driven by revenge and ignoring another Pro that needed saving, something that Iida admits post-battle was a bad move in hindsight.
- Xanatos Gambit: Stain and Tomura's "competition" turns out to have been this, set up by the real Big Bad. No matter what happened, Stain would be seen as being part of the League of Villains. This would connect his actions to theirs and give them a kind of publicity and legitimacy.
