Mei Hatsume/Synopsis

U.A. Sports Festival Arc
Mei Hatsume takes to the field with her classmates from the Department of Support. After the opening ceremony, Mei competes in the Obstacle Race.

When Ochaco Uraraka and Mina Ashido reach The Fall section of the course, Mei makes herself and all of her gadgets known. Mina questions why Mei is allowed to wear special gear, to which Mei replies she developed them herself and it allows for a more fair competition at the Festival because Hero Course students receive training. Mei uses her Wire Arrow and Hover Soles to cross tightrope-laced abyss with ease, laughing gleefully as she does it. She eventually finishes the race and places forty-first, qualifying her to compete in the Cavalry Battle.

While choosing teams for the Cavalry Battle, Mei spots Izuku Midoriya, the first place contestant, and confronts him. She pitches to join his team because all eyes are on him and if she joins him, then all eyes will be on her and her "babies" as well. Izuku is startled by Mei's assertive personality, but he is won over after she shows off several of her gadgets. Izuku even recognizes one from the Pro-Hero Airjet, and the two have a friendly discussion about it.

Once the Cavalry Battle begins, Izuku is forced to use the Jet Pack to escape pursuing teams. Mei asks how her gadgets perform and is joyous when Izuku replies her "babies" are amazing. After getting trapped by one of Minoru Mineta's spheres, Izuku is forced to break one of the hover soles, much to Mei's dismay. After finally getting away, Mei and her team are confronted by Team Todoroki.

Denki Kaminari attacks using his electricity, which short-circuits Team Midoriya's jetpack. When it fails to work and Team Midoriya are unable to flee from Team Todoroki, Mei comments that her baby needs some upgrades. Thanks to Izuku's strategy, Team Midoriya are able to evade Team Todoroki for the back half of the round. However, their luck runs out when Tenya Ida uses his special Recipro Burst technique to steal Mei's team's points in an instant. Mei agrees with Fumikage Tokoyami that they should try for other points, but Izuku refuses and they engage Team Todoroki again.

Izuku is able to steal one of their headbands, but Mei notices it is the wrong one. They try one more time to recover their points but run out of time as the Cavalry Battle ends. When Izuku tries to apologize for losing, Mei and Ochaco point him towards Fumikage, who reveals he was able to steal a headband worth enough points to advance. Team Midoriya takes fourth place, and Mei qualifies for the finals.

After a short break following the completion of the second round event, it is announced the sixteen qualifying students will duel in a one on one fighting tournament. Once the matchups are announced, she approaches "legs" to ask him if he's Tenya Ida, to which he confirms.

Mei offers Tenya Ida some of her equipment and tells him it is to keep the fight fair between them. Moved by her sportsmanship, Tenya agrees. However, when their fight begins Mei manipulates Tenya into showing off her gear while evading his pursuit. She uses her Quirk to keep an eye on the support company representatives as she transforms the battle into a commercial for her support items.

For the next ten minutes, Mei continues her fight while explaining the features of her items to the audience using a mic attached to her headgear. Satisfied with her exposure, Mei steps out of bounds and eliminates herself from the tournament, allowing Tenya to advance to the next round. Mei thanks Tenya for allowing her to use him and apologizes for it, much to Tenya's annoyance.

Final Exams Arc
Mei is mentioned by All Might; according to All Might, Mei's High-Density Weights won a competition, so they were used as the handicaps for the teachers to wear in the exams.

Provisional Hero License Exam Arc
Mei appears again as Izuku, Ochaco and Tenya visits the workshop to improve his hero costume. An explosion catapults her through the door and lands on Izuku as he tries to enter. She recalls Izuku only to turn away and tell him that she's busy in the workshop. However, upon hearing that Izuku wants to upgrade, she turns all her attention to him. While Power Loader and Izuku discuss how they can upgrade his costume, Mei grabs onto Izuku to feel his muscles. Mei equips Izuku with her 49th invention, a Power Suit. However, the armor moves independent from Izuku and hurts him, causing her to apologize for programming the range of motion incorrectly.

Upon hearing Tenya's request for a gadget that lets him cool his legs, Mei equips him with her 36th gadget, an arm brace with rocket motors, which promptly sends Tenya into the ceiling. When Tenya complains, since his quirk is located in his legs, she reasoned that he could run with his arms, to cool his legs. It is this suggestion that leads Izuku to develop his new set of moves, Full Cowl - Shoot Style, which utilize his legs more than his arms. Power Loader scolds Mei for her carelessness and she returns to her work, though he remarks that Mei is an outstanding student with a remarkable ability to invent. Shortly after, Mei tries to improve Ochaco's costume with some gadgets, much to Ochaco's dismay. In the end, Izuku settled for an arm brace that reduces the strain on his arm and boots with a coil-mechanism, that absorb some of the impact force of his kicks.

Later, Eijiro Kirishima and Denki Kaminari go to the workshop to ask Mei and Power Loader to improve their costumes. Denki in particular explains that he is unable to control the flow of his electricity by himself, so he asks them to design a device that allows him to control it. Mei and Power Loader accept his request and manufacturer for him the Sharpshooting Gear.

U.A. School Festival Arc
Mei is excited by the U.A. School Festival because it represents for the students who do not belong to the Hero Department the opportunity to shine. Mei decides to build her "Baby number 202", a large combat suit, with which she plans to attract the attention of tons of companies. She is so dedicated to this project that she does not even bother to bathe and she plans to clean up once her project is finished. She does not sleep much either.

During the weeks of preparation Izuku, along with Mirio and Eri, goes and sees U.A.'s Development Studio. Mei asks Izuku about his Hero equipment and to inform her if he needs anything. At some point, Izuku asks Mei to make him a pair of gloves that allows him to compensate for the strength of his hands.

Days later, Mei was out in the forest, following one of her latest gadgets and comes across Izuku and All Might who caught her device. All Might (while disguising his voice) catches her device and hands it back to her, as she states it was just acting up. Mei then notices Izuku and tells him the item that he requested is similar to one of her inventions and is customizing it for his use, to which he thanks her. Mei leaves while following after her device.

Later on, she finds Izuku training and tells him his new gloves are complete and gives them to him. She hands him the instruction manual for them before running off.

Shortly before the festival begins, Mei finally cleans and kempt herself. She presents her robot suit to several company representatives and, when the festival ends, she finally goes to sleep.

U.A. Traitor Arc
Sometime after the School Festival and before the Paranormal Liberation War, Mei was staying at U.A. High, still inventing new devices for the Hero Course.

After the fallout of the War and the downfall of hero society, Izuku, accompanied by Tenya, reunites with Mei to request a new costume upgrade, only to land in another deja vu moment where an explosion occurred right before he can answer the door and Mei lands on top of him.

Mei asks Izuku and Tenya what they need from her, with Izuku lamenting with embarrassment how his Danger Sense didn't activate. Tenya tells Mei they came looking for repairs for their Hero Costumes. Mei is confused why they don't just take them to the item agency, and Tenya responds that with recent disruption to the agencies, they have to rely on the support course. Mei's increasingly nonchalant reactions cause Izuku to realize that Mei has no idea what is going on outside.

Power Loader emerges from the explosions, once again berating Mei. Izuku hands Mei his Mid-Gauntlet, asking if she can fix it for him, but she immediately refuses due to the extensive damaged it has, so she'd have to create a new one, and they don't have enough resources required for the compression mechanism. Tenya then asks for repairs for his armor, but she shuts him down due to not having a spec sheet.

Tenya is surprised that Mei would turn down the offer due to how much she loves making things, as Izuku looks on to see her currently working on the evacuation shelter blocks. Power Loader tells them that Mei was brought on to help strengthen the barrier, and she's been busy creating new mechanisms in case of mass evacuation. Power Loader compliments her inventive mind, and she responds with how she always needs to try think up new "babies" to improve themselves.

Izuku compliments Mei on how focused and busy she is with her inventions that she had no idea how the outside world is, but Mei responds calling him dense, saying that even she is aware of the trouble Heroes are facing now. And while they aren't fighters, they're also doing everything they can to protect people; inventing stuff being how the support course does heroics.

Before Izuku can react, Mei throws a pair of Air Force Gloves attached to new make-shift Gauntlets right at his face, saying that she couldn't make an exact copy but it's the best she can do, surprising Izuku that she did that all with just her left hand. She proceeds to throw a new piece of armor for Tenya right at his face too, exasperating the support students that she did it all so fast. She concludes saying for them to tell the rest of the hero students that they'll all win this.

Final War Arc
With Tomura's completion approaching, the Heroes prepare for the Final War to defeat the army of villains led by All For One. As the Heroes continue their preparations to split up and deal with the villains individually, Mei proposed an idea of how to deal with Tomura Shigaraki, transforming U.A. into a flying fortress. She was able to come up with a way to make use of the evacuation and anti-Decay measures Nezu had set up, as well as dividing the ground into smaller blocks and giving them drone-like properties.

Mei, her Development Course students, Power Loader, Cementoss, and Ectoplasm got to work on creating the fortress in time for the Final War. Tomura was teleported to U.A. transformed into a flying sky fortress, a "coffin" designed only for Tomura which he can't escape and that they can control. Whenever he attempts to Decay the ground, the pieces fly up into the air to disintegrate safely, while new pieces are quickly rebuilt and replaced.

The team remain adamant to constantly keep the fortress afloat, constantly working to repair any pieces destroyed in the battle between Tomura and the other Heroes. To assist them, Momo Yaoyorozu uses her Quirk to keep on replenishing new supplies for them to rebuild.

While she continues to work on maintenance of U.A., she is completely oblivious to all the events that are happening on the surface, including Katsuki unleashing a fully direct blast of his Explosion that reverberates both the inside and outside of the Fortress, which are felt by everyone else,, and Izuku's return to the battlefield to fight Tomura. Unfortunately, the battle starts to fall apart as a freed Kurogiri teleports Twice Doubles to the observation deck where Shota Aizawa and Neito Monoma are stationed, causing them to be attacked an undoing their use of Erasure on Tomura.

This results in Tomura unleashing a massive explosion, destroying most of the fortress. Inside, Power Loader reports to all the students and staff that they can no longer maintain spare parts as the surface was completely destroyed. Mei asks about the power line for the electric barrier, and Power Loader replies that it's busted and the electric barrier can no longer stand at full output. Mandalay then reports to everyone that Skeptic has hacked into their system, and they have lost control of the flight system, causing the fortress to start to fall to the ground, heading on a collision course to crash into a nearby coastal city. As U.A. continues to descend into a nearby coastal city, they are saved when it suddenly stops, thanks to the intervention of Gentle using his Quirk to save it.

Despite Gentle's intervention, the sheer weight of the fortress was too much for Gentle, and all of the students and staff are being overrun by the Twice Double ocean. With all the damage Tomura had inflicted, Mei is working as fast as possible to get the systems back up and running. Momo creates makeshift weapons and armor to protect Mei from the Doubles while she was doing repairs. Using her Quirk, she created machine guns, rocket launchers, armor, and a staff to fend off agents the endless Twice Doubles until Ochaco succeeds her mission to defeat Himiko, and as the result of Himiko's limit, the Twice Double ocean starts to crumble and disappear.

Momo noted that the Twice Doubles are fading, and Mei informs her that U.A. is much lighter so they can keep floating as she completes her repairs. While finishing up the repairs, Mei was unaware that Izuku had jumped down from U.A. with Tomura, bringing their battle down to the surface.