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Fanfic / Dekiru: The Fusion Hero!

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Collage of Katzuku, the first of many Fusions. Art Provided by bluecrysto.

Dekiru: The Fusion Hero! (AO3 link) is a My Hero Academia fanfiction by | OmegaInfinity | where Izuku can fuse himself with inanimate materials and other people.

Izuku was so excited when he manifested his Quirk. Being able to combine with objects to make himself stronger? So cool! However, what he didn't expect, what no one expected, was what happened if he used his Quirk on people... (Or, What if Izuku's Quirk was a combination of Kevin Levin's Osmosian ability and the Fusions from Dragon Ball Z and Steven Universe)?


Dekiru: The Fusion Hero! provides examples of:

  • Accidental Innuendo: In-Universe example. As Izuku got older, Fusion started to mean something more perverted and laughable than it actually was to his peers, which led to him getting mocked throughout middle school. Ochako made it a point to go straight to Izuku's house rather than tell her parents what happened during the Entrance Exams because she was afraid they'd get the wrong idea.
  • Adaptational Nice Guy: Katsuki is much nicer in this fic, as a result of Izuku developing a Quirk when they were kids and others still bullying him for it, Katsuki became Izuku's Only Friend for a long time. While he can still be a bit of a jerkass in the present, he comes across more as a Jerk with a Heart of Gold to Izuku and, later, Ochako.
  • Adaptation Relationship Overhaul: Any animosity Izuku and Katsuki have in canon is nonexistent in this fic, and they are bonafide friends who support one another. Ochako and Katsuki are also much closer, being Vitriolic Best Buds.
  • Adult Fear:
    • The first time Izuku and Katsuki fused into Katzuku, it terrified their mothers, whose sons had seemingly disappeared and left a completely unknown boy in their place. Even after figuring out what happened, their terror remained due to the possibility that the fusion might have been permanent.
    • Aizawa is understandably horrified when Nomu goes after Tsuzuru, because that means the thing that beat him bloody is now chasing after someone who is effectively three of his students.
  • All Your Powers Combined: The unique Quirks wielded by Izuku's human fusions (referred to as "Quirk Mutations") are all variations of their parent-component's Quirks, making them more flexible and powerful. This is also on top of being able to use the strength of One For All. Such mutations include:
    • Katzuku (Katsuki Bakugo): "High-Ex." Same explosive ability as Katsuki, but the explosive sweat can be excreted from any part of his body and is twice as powerful.
    • Izuchako (Ochako Uraraka): "Gravity Manipulation." A level of gravity control both on herself and objects around her much more powerful that Ochako's, to the point of it being easy to confuse it for telekinesis. Nausea weakness is still present, but not as much as if it were Ochako alone.
    • Moku (Momo Yaoyorozu): "Transmutation". Combining Momo's Creation with Izuku's Fusion, Moku is able to turn her body into any material she can think of, no outside materials needed! In addition, objects made with Creation take less energy and effort to create.
    • Izuna (Mina Ashido): "Acid Control." Can excrete acid, but can excrete far more than Mina can and the viscosity and corrosive properties of the acid can be manipulated after it has been administered on-command.
    • Izoru (Minoru Mineta): "Sticky Bomb." The orbs at the end of Izoru's hair explode upon impact, creating a shower of super-sticky fluid that glues any touching objects together except for himself at his own choosing. Izoru can also determine the size of the orbs prior to plucking them from his hair, though larger orbs take longer to create.
    • Tsuku (Tsuyu Asui): "Poison Dart Frog." The irritating compound in Tsuyu's mucus becomes much more toxic, allowing her use her tongue for precision strikes that cause an almost-instant complete loss of motor control temporarily. The mucus from her skin has the same effect, but is slower-acting.
    • Tsuzuru (Tsuyu Asui and Minoru Mineta): "Sticky Mucus." Tsuzuru's body naturally creates a clear variant of Izoru's Sticky Bomb solution, nearly invisible but just as strong. It is naturally part of her saliva and can be secreted from her skin.
    • Katzuchako (Katsuki Bakugo and Ochako Uraraka): "Explosive Touch." If he touches an object with all five fingers, he can charge it with energy and prime it to explode, with bigger objects leading to bigger explosions.
  • Almighty Janitor: According to All Might, Nana Shimura, despite being the strongest hero of her era, never came close to breaking the top one hundred in hero rankings. Before All Might, none of the One For All users were ever close to high in the rankings since being the best was trivial compared to protecting others. All Might himself only bothered with becoming the Number One hero because it better allowed him to spread hope to the common citizen and dread in the common criminal, reducing crime rates and thus, theoretically, saving even more people.
  • Amazonian Beauty: Tsuku, Tsuyu and Izuku's fusion, is described as being very tall and noticeably muscular.
  • Armor-Piercing Response: In respone to Todoroki insulting Human Fusion, Izuku asks "What do you want me to do, only use half of my Quirk?".
  • Beach Episode: Chapter 13, which is even titled A Beach Reprieve. A day at the Dagoba Beach is a chance for both some fun, further training, and even making a new Fusion.
  • Berserk Button:
    • Katsuki, being Katsuki, has many, but a major one is disparaging Izuku's Quirk. For years Katsuki has been trying to convince Izuku about how great his Quirk is, and now that they're at U.A., he won't stand for anyone putting down his best friend when he's finally proved all his nay-sayers wrong. On a more minor note, he gets easily annoyed when anyone other than Izuku calls him "Kacchan"... and unfortunately for him, anyone who fuses with Izuku tends to start calling him that.
    • Human Fusion becomes this for Shoto after Moku defeats him and Tenya in the Heroes vs. Villains exercise. His expression darkens every time it's mentioned within his earshot. He brings up Izuku's seeming reliance on Human Fusion just before the Sports Festival to see if it's going to be used, becoming angrier as people defend it and reaching room-chilling anger when Izuku says "What do you want me to do, only use half of my Quirk?"
  • The Cameo: Satsuki, Tsuyu's little sister, appears in Chapter 13 as Tsuyu brings her along at Dagoba Beach.
  • Cast From Stamina: It's implied that how long Izuku can stay in a fused state is based on stamina, as especially draining moves can eat through his transformation time faster than is normal. Three-person fusions seem particularly bad about this, when Tsuzuru reverts back to Izuku, Minoru, and Tsuyu, the latter two are tired and sore, but it pales in comparison to Izuku's state, as he's literally steaming and covered in sweat and reddened skin, though he recovers quickly, and feels like he's just been training for hours. Fusing into Katzuchako is even worse, with Izuku, Katsuki and Ochako left exhuasted, dehydrated and with low-blood sugar afterwards.
  • Chrome Champion: This is Izuku's most preferred Material Fusion. If enough metal is on hand, Izuku can fuse his entire body with it, turning him into this. Thanks to his costume having metal woven into it, he can do this on the fly. Moku, Izuku's fusion with Momo Yaoyorozu, can do the same, but without the Elemental Baggage.
  • Color-Coded for Your Convenience: Whenever Izuku uses Material Fusion, he glows a light green color. Whenever he uses Human Fusion, however, both he and his partner glow their own personal colors.
  • Crippling Overspecialization: Discussed with Aizawa, who admits to Izuku and his friends that had Izuku went to Human Fusion as his first choice, he would've been considered a potential one-trick-pony and been expelled, along with whichever friend enabled him. Aizawa says that Human Fusion is incredibly powerful, but he doesn't want Izuku to make a habit of using it as he might be left defenseless if there's no-one around to fuse with. Izuku himself is aware of this, and makes it a point to use Human Fusion only as a last resort.
  • Curb-Stomp Battle: All Might takes down the villains at USJ so fast that they don't even have time to surrender before he plants them in the ground.
  • Cuteness Proximity: Satsuki has this effect on Ochako and Mina, who can't help but gush about cute she is whenever she's with them, and they go all "awwwww" whenever she does anything.
  • Dangerous Forbidden Technique:
    • Human Fusion is treated like this. While it isn't explicitly forbidden, its unpredictable nature (there is no way to know what powers a fusion with another person will have if said fusion has not occurred before) means it's best used only as a last resort. Not to mention that prior to gaining some tips from Mandalay, Izuku ran the risk of exposing All Might's secret due to its Mental Fusion nature. Notably, the first time Izuku starts spamming the technique in a short time-frame is during the USJ arc, which is an explicit life-or-death situation.
    • Multi-person fusions are even worse than regular Human Fusion. While the fusions are more powerful, they drain even more stamina from all the component partners (especially Izuku) and can't be held together for long. Holding one for longer than it should be results in the fusion draining all the people who are part of it. Izuku, Katsuki, and Ochako end up suffering severe dehydration, low blood sugar, heatstroke, and torn muscles from overclocking their fusion. In addition, while Izuku trained to keep his thoughts separate to keep One for All hidden, his fusions and fusion partners haven't, and Tsuyu learns about One For All through her triple fusion.
  • Destructive Savior: Subverted. When prepping for Aizawa's Quirk Assessment Test, Izuku tries thinking of something he can fuse with, and thinks of the walls of the building... only for him to realize that no, ripping chunks out of buildings is probably not the best first impression for a hero to make.
  • Didn't See That Coming: Human Fusion gets this reaction a lot.
  • Didn't Think This Through:
    • Aizawa probably shouldn't have let the girl whose power is "turns off gravity" go first in the ball throw test. They never get that ball back.
    • Izuku had his hero suit designed so that he'd have enough metal to fuse with his entire body at any time, but he didn't realize that doing so would consume most of the substance of the suit and leave him largely Exposed to the Elements, which is a problem in the Heroes vs. Villains exercise, where he's paired off with Momo against Shoto and Tenya. All Might caught this but decided to let him discover it himself so that it'd be a learning experience for him.
    • Shoto himself just froze the entire building without thinking of a backup plan if the other team had a way to bypass this despite Tenya trying to convince him to come up with one before they started.
      • He also didn't take into account whether or not the building would be able to withstand the weight from the ice he was creating, allowing his opponents to further destabilize it on purpose, and by freezing himself in the room with the bomb in it to guard it, he left himself blind to what was going on outside.
  • Does Not Know His Own Strength: What happens when Tsuzuru jumps while combining Tsuyu's frog legs with One For All - the result sends her flying so high she crashes into USJ's dome ceiling.
  • Drama-Preserving Handicap:
    • Using Fusion to boost Izuku's durability means that using One For All won't destroy his arms every time he uses it, so that's a plus. However, it seems to also limit its power somewhat, keeping him from just using a Megaton Punch with every blow. He can still launch extremely powerful blows, what would normally be considered a Megaton Punch and what would have outright crippled his arms after one use in canon, but it's not the One-Hit KO that it normally is.
    • Human Fusion is given many drawbacks (Cast From Stamina, memory-sharing, pain-sharing, and unpredictability) to make it a Dangerous Forbidden Technique, because otherwise it would be a Story-Breaker Power, especially with One for All added to the mix. Even now with the drawbacks, the technique is powerful enough that Aizawa was genuinely worried Izuku would come to rely on it too much.
  • Draw Aggro: This is Katsuki and Ochako's strategy in the Heroes vs. Villains exercise: Katsuki assaults the villains from the front and gets them to focus on him, Ochako sneaks in through a window and captures the weapon. Interestingly enough, in canon that's what Izuku and Ochako did against Katsuki, exploiting his Leeroy Jenkins tendencies.
  • Dynamic Entry: How Tsuzuru saves Aizawa from Shigaraki during the USJ attack, launching herself down from the facility's roof and hitting the villian square in the face.
  • Early-Bird Cameo: The leader of the Wild Wild Pussycats, Mandalay, sends Izuku some tips on how to avoid sharing thoughts with those he fuses with as a favor to All Might.
  • Elemental Baggage:
    • As shown during Aizawa's test, Izuku needs quite a lot of material on hand to absorb to fully transform, else he can only manage Partial Transformations. However, Momo Yaoyorozu can easily provide said material, making her Quirk a perfect complement to his.
    • Izuku manages to use this facet offensively during the U.A. Entrance Exam, by absorbing the chassis of one of the testing robots into armor for himself and leaving the harmless internals behind.
  • Elemental Shapeshifter: Moku, Izuku's and Momo's Fusion, is able to transform into any material that she can think of thanks to Momo's Quirk, with no outside material required.
  • Embarrassing Nickname: Katsuki barely tolerates Izuku calling him "Kacchan", but he absolutely hates when everybody else starts doing it.
    • Izuchako understandably doesn't like being called "Floaty Deku" by Katsuki.
  • Emergency Transformation: Non-permanent variant — Izoru, Izuku and Minoru's Fusion, fusing again with Tsuyu to save her from Shigaraki's touch.
  • Eureka Moment: Izuku has one when he realizes that he can use his Fusion Quirk to merge with something tough enough to increase the durability of his bones to the point where he can withstand using One For All without breaking them. He wonders whether he should be feeling smart for thinking of it or dumb for not doing so earlier.
  • Exposed to the Elements: The result of Izuku absorbing his costume, which he's heavily embarrassed by.
  • Failed a Spot Check:
    • Katsuki and Izuku are so glued at the hip neither notice the memory sharing aspect of Fusion until after Ochako finds out about All-Might and One For All. They're only able to confirm it by checking to see what each other had for breakfast.
    • Katsuki is so distracting to their foes during the Heroes Vs. Villains exercise that Ochako was able to simply float herself up into the bomb room through a window and over their heads to the bomb, and Sato and Koda didn't notice until the match was already over.
  • Fire-Forged Friends: Literally. Every time Izuku fuses with someone, the Mental Fusion fosters a familiarity between him and them that remains after they de-fuse. This also applies to multi-person fusions, for all the component partners.
    • His friendship with Ochako accelerates even faster than it did in canon, to the point that she can be considered his best friend after Katsuki in a mere matter of weeks.
    • When Moku de-fused, Momo started addressing Izuku by his first name instead of his last name like she previously had at the start of the "Heroes vs. Villains" exercise, and they shows signs of starting a close friendship as well.
    • After Tsuzuru de-fused, Minoru and Tsuyu not only started addressing Izuku by his first name, but also each other by first names. Their interactions were also a lot more casual, bordering on Vitriolic Best Buds. Izuku himself has no issue calling Tsuyu "Tsu" after the fusion, something his canon self still has difficulty doing.
  • Flipping the Bird: Katsuki does this to his and Izuku's middle school class on the last day of school, as part of him telling them off for doubting Izuku.
  • For Want of a Nail:
    • Katsuki is on much better terms with Izuku here, and Izuku's presence has helped curb his more aggressive tendencies.
    • Izuku fusing with Ochako has made her aware of One For All, letting her in on the secret of the Quirk and having her learn All Might's dwindling power much earlier than in canon.
    • Thanks to having Ochako and Katsuki as his sounding boards, Izuku's costume design is slightly different than in canon. In particular, the hood and mouth guard are absent due to them noticing he'd look like an All Might copycat, and most of the material is composed of woven metals. Visually, it's described as being nigh-identical to his alpha costume in canon, simply without the mask and hood.
      • Likewise, Ochako and Katsuki have their costumes altered. Ochako's suit is more form-fitting to allow for easier movement with her Quirk, and Katsuki has several smaller bomb tanks on his gauntlets instead of one big one.
    • The Hero vs. Villain exercise has several changes to the teams this time around. Izuku is partnered with Momo this time, while Ochako is partnered with Katsuki. This in turn causes Tenya to be partnered with Shoto, and Minoru to be partnered with Shoji.
      • The first match is also different. Tenya and Izuku are in the same roles as canon, whereas Shoto is on the villain team this time, while Momo is on the hero team. Katsuki is also on the hero team for his match, opposed to being on the villain team like in canon.
    • Thanks to fighting Tenya in melee combat during the Hero vs Villain exercise, Momo is made painfully aware of her lacking skill in hand to hand combat compared to her contemporaries.
    • Sato is the one who escapes from the USJ attack to warn the faculty instead of Tenya, which means that help takes longer to arrive since Sato doesn't have Tenya's Super Speed. Tenya is instead sent to the landslide zone, in place of Katsuki. As a result, All Might isn't there in time to defeat Nomu, forcing Izuku to initiate a second triple-fusion with Katsuki and Ochako to hold Nomu off until help arrives.
    • Nomu is ultimately defeated by damaging it enough that its Healing Factor just can't keep up anymore, before All Might even arrives.
  • Fusion Dance: Obviously! Izuku's abilities takes direct inspiration from Kevin Levin's Osmosian abilities in Ben 10, and the fusion properties of both Dragon Ball and Steven Universe.
    • With materials, Izuku needs enough material to completely fuse with, or it ends up just being partial fusion, such as the first time he activated it and turned his hand into plastic when he fused with an All Might action figure.
    • With other people, it's a Composite with Power Booster elements, as it enhances the Quirks of the participants. It also has downsides - it doesn't last forever, the injuries suffered by the fusion happen to both elements (unless Izuku or one of the other parties pulls them into themselves), and it requires two people to do human fusion. It also has a Mental Fusion aspect as well, and the thoughts and memories of one person can be shared with the other. This isn't normally bad - after all, Izuku and Katsuki have been doing it for years - but if you know something sensitive, like All Might's secret, that can prove problematic.
    • During the USJ arc, Izuku finds he can create three-person fusions, which he does with Minoru and Tsuyu, and then later on with Katsuki and Ochako.
  • Gender Bender:
    • Since the resulting fusion between Izuku and Ochako is a girl, Mitsuki points out that, by extension, Izuku turns into a girl when fused with Ochako.
    • Fusions with Momo and Mina are both girls as well, leading Katsuki to declare that the gender of his Human Fusion partner determines the fusion's gender, so any time he fuses with a girl will result in this.
    • Three-person fusions are harder to predict, since while Tsuzuru (Izuku, Tsuyu, Minoru) is a girl, Katzuchako (Katsuki, Izuku, Ochako) is a boy.
  • Godzilla Threshold: During the USJ arc, Izuku initiates a second triple-fusion with Katsuki and Ochako, despite having only just learned he could do it that day (and by accident, no less), to hold off Nomu until help arrives. He knows he's risking severe, potentially fatal, exhaustion in doing so, but the circumstances are so dire that it was the only option available if all of Class 1-A (including Aizawa and Thirteen) were to survive. In return, Katsuki and Ochako don't fight him on this despite being the most vocal opponents of his self-sacrificing tendencies, because as much as they hate it, they know he's right.
  • Good Thing You Can Heal: Trapped in Tsuzuru's adhesive, the Nomu proceeds to just rip off its trapped flesh and let its regeneration take care of it.
  • Heroic RRoD:
    • Triple-fusions are ridiculously powerful but exhaust Izuku much faster than normal, not to mention open the door to people learning about One for All again.
    • Denki unleashes a massive blast to take out most of the villains surrounding him, Jiro, and Momo but doing so leaves him befuddled for several minutes and barely able to use his Quirk afterwards.
  • Heroic Self-Deprecation:
    • The mockery from his classmates for his Fusion Quirk has given Izuku a bit of a complex about it, and although he's gotten a bit better about it, he still has trouble seeing much value in it sometimes, as mentioned below.
    • Minoru's just as bad as Izuku, if not worse, as even after seeing how Izuku's Fusion Quirk enhances others, he was convinced that it would just make his Pop-Off Quirk more useless than it already was. Izuku makes it a point to dispel this notion.
  • Heterosexual Life-Partners: Unlike in canon, Izuku and Katsuki have an almost sibling-like closeness in this story. Although, this actually ends up hurting them in the long run. Since they're such good friends, they spend literally almost all their time together. When Izuku fuses with Ochako to make Izuchako, they don't realize that memories are shared between the fusion's components because for the most part, there wasn't any overlap - they spend so much time together their memories are nearly identical. They check by trying to remember what the other had for breakfast.
  • Hour of Power:
    • Izuku cannot hold a fusion (material or human) for more than a while before separating, though practice slowly builds up the limit. It's also implied that it's based on stamina, as using draining moves (like One For All) can shorten the timespan.
    • Three-person fusions are extremely strong, but apparently burn through the allotted time much faster than normal. Tsuzuru's components split well before the normal limit, and they're heavily exhausted.
  • Ho Yay: In-universe. Izuku got a lot of flak about this with his Quirk in middle school due to his usual fusion with Katsuki, and his classmates taking it in newer contexts as they got older. At one point Izuku wonders if they even remember that he can fuse with materials as well.
  • In Spite of a Nail:
    • Despite having a Quirk, Izuku still has doubts about being a Hero with it due to his classmates mocking him for it, finding it creepy. Luckily, Katsuki is fully supportive of him this time around.
    • All Might still meets Izuku under the bridge and becomes interested in him as a successor.
    • Despite Fusions sharing the pain and therefore lessening the feedback they'd receive from using One For All, Izuku still destroys his arm during the entrance exam by taking all the feedback onto himself rather than letting Ochako take any of the pain.
    • Just like in canon, one of the top students of Class 1-A eats a big helping of Humble Pie after losing the Heroes vs. Villains exercise. Though, in this case, it's not Katsuki (whose ego is much more manageable compared to canon), but instead Shoto, who is defeated by the fusion of Izuku and Momo. Shoto was even teamed with Tenya, like Katsuki was.
  • Instant Sedation: Tsuku, Tsuyu and Izuku's Fusion, has paralyzing mucus that can take effect almost instantly when she uses her tongue to apply it. The mucus from her skin is slower-acting.
  • Jerkass Has a Point: Katsuki is more of a Jerk with a Heart of Gold here, but he still makes some good points.
    • He chews out Izuku for taking on all the damage his fusion with Ochako took on instead of splitting it like what normally happens. All Might agrees with him, pointing out that in a combat scenario, two moderately injured heroes are better than one intact one and one incapacitated one.
    • When they realize that All Might used up his available time in his hero state before the training mission at the USJ, Katsuki calls him an idiot, pointing out that, unless some major incident happened that they somehow didn't hear about in the news, nothing happened where he needed to pitch in, especially since he knew what the class was doing that day, so he should have had some time left for it. Izuku, try as he might, can't come up with a good defense for his mentor.
  • Jumped at the Call: Mina is actually really unexpected for Izuku, as she's the first person to volunteer to fuse with him. Katsuki fused with Izuku first on accident, Ochako was fused with to save her from the zero-pointer, and Momo did accept, but Izuku offered first.
  • Logical Weakness:
    • When using Fusion on inanimate materials, Izuku is only able to fully transform himself if has enough material to do so, and he's only as tough as said materials. The converse is also true: there is only so much of his body that he can merge material with, so if the source of the material is too substantial (like, say, the large and thick metal doors of the USJ), he can't absorb all of it.
    • Aizawa's Quirk nullifies other people's Quirks. When he uses it on a fusion, the fusion splits apart instantly.
    • According to Izuku's notes, his fusion with Katsuki, Katzuku, sweats a lot more than a normal person with less effort, meaning that he tires quicker and can quickly become dehydrated if he overuses it.
    • Izuku learns mental exercises to keep those he fuses with from learning certain secrets, such as All-Might's identity as Toshinori Yagi, but Izuku's fusions don't use those exercises so when Izoru fuses with Tsuyu, she learns about All-Might's Secret Identity and about One For All.
  • Loose Lips: All Might, while chatting to Izuku after the exam, accidentally lets slip to Izuku that he passed before the official results come out. He tries to Verbal Backspace, but Izuku's Puppy-Dog Eyes eventually wear him down.
  • Ludicrous Gibs: Katsuki's Explosion Quirk wasn't enough to do this to the Sludge Villain, but Katzuku's High-Ex is more than capable.
  • Mass "Oh, Crap!": All the remaining villains at the USJ have a moment when All-Might arrives.
  • Mental Fusion:
    • A fusion merges personality traits from both Izuku and whoever he fuses with. In Izuku's case, this means that the majority of the fusions have a tendency to Motor Mouth (whether boastfully like Katsuki, outgoing like Ochako, or exuberantly like Mina) and call Katsuki "Kacchan".
    • However, this also allows their components to involuntarily learn secrets and details about each other, such as All Might's secret. Izuku is currently taking tips from Mandalay about keeping thoughts separate, and it hasn't been made clear yet if Momo (or any of the other people Izuku has fused with since her) has retained any stray thoughts from the fusion.
    • On top of that, it seems that people who fuse with Izuku adopt some of his personality traits and quirks (But not the other way around). For example, Ochako and Momo started calling Katsuki "Kacchan" (much to the latter's utter annoyance) like Izuku does.
  • No Conservation of Energy: Averted. The steam Izuku and others let off from overdoing a fusion is water from their bodies, resulting in dehydration.
  • Not Quite Dead: The Anti-All Might Nomu has just been dumped into USJ's lake glued to a mass of metal, with no way for him to escape. Then Kurogiri retrieves his body from the lake, and it looks like he has drowned. Then he twitches.
  • Normal Fish in a Tiny Pond: Played with in regards to Shoto. While he's still the strongest student in Class 1-A in terms of raw power, all of them still have versatile and unique Quirks that are better for other aspects of hero work than his would be. Then there's Izuku's fusions, which not only surpass Shoto in power but also make his classmates' Quirks even more versatile, completely upstaging Shoto in turn.
  • Oh, Crap!:
    • Izuku, Katsuki and All Might have a collective one when Izuku's first use of One For All at the beach almost obliterates his arm.
    • Izuku has a MASSIVE one when he realizes that fusions share memories, meaning that Ochako had learned about One for All and the truth behind All Might. Fortunately, she agrees to keep the secret.
    • Two times in quick succession:
      • Izuku, Minoru and Tsuyu when Kurogiri overhears Minoru mentioning where the Nomu was, which allows him to retrieve him.
      • Then a Mass "Oh, Crap!" version when the Nomu who looks like he had drowned in the lake turns out to still be alive.
  • Partial Transformation: What happens if Izuku doesn't have enough material to fuse with. His first fusion turned his hand into plastic when he accidentally fused it with an All Might action figure.
  • Portmanteau: All of Izuku's Human Fusions have this sort of name.
  • Pride Before a Fall: Instead of Katsuki, this happens to Shoto during the Heroes vs. Villains exercise. He arrogantly believed that his ice would be enough to win the match for his team within the first minute, like he did in canon. Instead, Momo and Izuku manage to bypass his ice easily. Once he realizes that failed, he sends Tenya out to fight them while he creates a massive and thick ice room to surround him as he guards the bomb, convinced that will be able to hold them off. He was correct... until they fused into Moku. Moku promptly defeats Tenya, then destroys the supports of the top floor of the building, sending his ice room flying into the air, where it breaks apart upon contact with the ground. Moku then captures the now freed bomb with seconds to spare. Shoto doesn't take the loss well, to say the least, especially after he learned it was a fusion of Momo and Izuku that won the match in place of them.
  • Psychic Block Defense: All Might has Mandalay send Izuku tips on making one so that the people he fuses with don't keep learning important secrets.
  • Punched Across the Room: What happens to Shigaraki after he tries messing with one of Izuku's Fusions, Tsuzuru.
  • The Rival: Katsuki has two this time around: Izuku as the holder of One For All and the person he strives to keep ahead of, and Ochako for edging him out as the highest scorer in the U.A. entrance exam (since she was given Izuchako's Rescue Points alongside Izuku).
  • Romantic Fusion: Izuchako, the fusion between Izuku and Ochako. Unlike the Trope Codifier Stevonnie and most examples, Izuchako is a girl. Like Stevonnie, they sometimes fuse without realizing, such as when they were celebrating passing the admission exam.
  • Screw This, I'm Outta Here!: After Tsuzuru humiliates him and All Might fails to show up in time, Shigaraki decides to ditch the USJ entirely alongside Kurogiri, completely fed up with how much of a failure his plan was.
  • Sore Loser: After his plan fails on every level, Shigaraki decides to bail with Kurogiri... but not before leaving Nomu behind to kill everybody in the USJ.
  • Stating the Simple Solution: When Shoto freezes the building in the Heroes vs. Villains exercise, Momo just makes ice skates at Izuku's suggestion. She's actually a little embarrassed that she didn't think of it herself, especially since she's had skating lessons. Izuku, for his part, is durable and strong enough in his metal form to simply barge through the ice by himself.
  • Stealth Hi/Bye: Tsuyu pulls this on Mina and Kirishima on their way to Dagobah Beach on chapter 13. They need a moment to realize that Tsuyu wasn't there a second before.
  • Story-Breaker Power: Even with Drama-Preserving Handicap at play, Human Fusion edges dangerously close to this, especially now that Izuku has inherited One For All. With there being so many different heroes with unique Quirks that Izuku can fuse with when he finally goes pro, there is theoretically no limit to his power — he can literally do anything.
  • Stripperiffic:
    • Izuku's first costume is an accidental version of this. The silver areas are actually woven metal that he can fuse with, but when he designed it he failed to take into consideration exactly how much fabric would be left after he absorbed the metal. It still covers enough of him to not be indecent though.
    • Momo has this as well, though hers is deliberate to take advantage of her Quirk. The more skin is exposed, the more area she can produce materials from.
    • Moku, the fusion of Izuku and Momo, also counts as this, though to a slightly lesser degree thanks to having Izuku's overcoat over Momo's leotard.
  • Stupid Sacrifice: Discussed regarding damage taken by Izuku's fusions upon defusing, specifically when Izuku took all the damage sustained by Izuchako onto himself instead of splitting it like he usually does with Katsuki, leaving him incapacitated with a broken arm and nausea while Ochako remained uninjured. All Might says that while his choice is noble, it is also unwise in some cases, such as in the middle of a battle where it's a better choice to have two injured but still active heroes than one uninjured hero having to protect an incapacitated one.
  • Super Empowering: When Deku fuses with an individual, in addition to gaining One For All's Super Strength, their Quirk becomes more powerful for the duration. Izuku calls these Quirk Mutations.
    • Katzuku's High-Ex mutation is a stronger version of Katsuki's Explosion Quirk, and he can bypass the limitation that makes it so that he has to secrete the nitroglycerin sweat via his palms and sweat it from anywhere. On top of that, the nitro-glycerin that he sweats is highly concentrated, so his explosions are over twice as strong as Katsuki's.
    • Izuchako turns Ochako's Zero-Gravity Quirk into full-on Gravity Manipulation, giving her the ability to control the movement of what the Quirk affects, akin to Mind over Matter, giving herself Flight, and negates the nausea that normally accompanies its use, at least to an extent.
    • When fused with Momo, their fusion Moku, along with using Momo's Creation Quirk with less energy and effort than Momo by herself, has a Transmutation mutation to turn herself into any material that she can think of, no outside material needed.
    • Izuna, Izuku's fusion with Mina, gives her Acid Quirk an Acid Control mutation. She can produce more acid than Mina can by herself, and she has complete control over its corrosive properties even after it's produced, making it go from harmless to hyper-corrosive with a simple thought. Her control is such that she can mentally acid-etch shapes and images into surfaces with surgical precision.
    • Minoru's Pop-Off Quirk merely produces very sticky hairballs, but his and Izuku's fusion Izoru turns those hairballs into Sticky Bombs filled with purple adhesive ooze. Moreover, because the balls are clumped at the ends of his hair rather than stuck directly to his scalp, he doesn't suffer Minoru's weakness of scalp bleeding.
    • Tsuzuru, Izuku's Fusion with both Minoru and Tsuyu, imbues Tsuyu's frog mucus and saliva with Minoru's stickiness, rendering it nearly invisible and strong enough to incapacitate the anti-All Might Nomu.
    • Katzuchako, Izuku's Fusion with Katsuki and Ochako, combines Katsuki's explosions with Ochako's five point touch activation of her quirk, which means he turn anything he touches into an explosive. It's strong enough to take on Nomu.
    • Tsuku, his fusion with Tsuyu, has the latter's mucus get upgraded to the point that her tongue can be used to paralyze someone on contact almost instantly.
  • Super Not-Drowning Skills: Its Healing Factor allows the Nomu to survive being submerged deep underwater glued to heavy metal by an inescapable adhesive for several minutes before being rescued.
  • Super Toughness: Izuku realizes that he can use his Fusion power to increase his durability and use One For All without injury, though seemingly at the cost of less power than if he was flesh and blood.
  • Superpower Lottery: Izuku, even more so than Shoto, who was specifically conceived with the intention of him winning the lottery. With Human Fusion, Izuku theoretically has no cap to his power and can more or less do anything if he fuses with the correct partner (or partners). Combined with One for All, it's almost a guarantee that he'll one day be the strongest hero in the world, bar none.
  • Tempting Fate:
    • During the first Hero Class and the Hero vs. Villain exercise, Izuku thinks he'll be okay as long as he is on a team with Katsuki or Ochako who he can fuse with without any drama. Guess who's not only not on his team, but paired up with one another?
    • When asked where the Nomu went, Minoru eagerly exclaims that their triple-fusion with Tsuyu, Tsuzuru, dropped him into the lake glued to a mass of steel. Unfortunately, Kurogiri hears him and makes a portal to get him out.
  • That Came Out Wrong: Kaminari's reaction to his wording when he's talking to Izuku about what happens to the individual fusion components when Izuku fuses with someone.
    Kaminari: Yeah, like, are you stuck in the fusion's head or something? Or do you just... cease to be for a little while? (Beat) Okay, that came out creepier than I meant it to.
  • Tongue Trauma: What happens when Tsuzuru takes a long fall and tries to catch herself with her Overly Long Tongue while remembering that Tsuyu's tongue isn't sticky enough to catch - and jerking to a sudden halt when it does catch thanks to Izoru's added stickiness to the Fusion's Quirk.
  • Training from Hell: Izuku's training from All Might as in canon counts, but Katsuki takes part in it alongside him this time.
  • Tranquil Fury:
    • Shoto goes from stunned disbelief to this once he learns that he lost to Moku, the fused form of Momo and Izuku, during the Heroes vs. Villains exercise.
    • Shigaraki is clearly in this state while confronting half of Class 1-A at the USJ's main staircase, after his plan proves to be, as he puts it, "a wash".
  • Underestimating Badassery:
    • Shoto massively underestimates Izuku and Momo during the Heroes vs. Villains exercise, and it costs him when their fusion Moku defeats him and Tenya. Tenya actually warned Shoto about this, but he wouldn't listen.
    • Just like in canon, the League of Villains towards Class 1-A. Their failure to read up one the kids' Quirks bites them in the ass when the kids prove to be far stronger than the thugs can handle. Combined with Izuku's Human Fusion, Class 1-A is even able to hold off Nomu.
  • Vitriolic Best Buds: Adaptational Nice Guy he may be, but this is still Katsuki we're talking about. He still considers Izuku and Ochako his rivals, and the two aren't averse to throwing barbs back at him. Despite this, Katsuki and Izuku are practically brothers, and Katsuki and Ochako form a friendship in the time before the semester begins.
  • What Kind of Lame Power Is Heart, Anyway?: Izuku has a bit of a complex about Fusion at first, in part because his schoolmates gave him a lot of crap about it, especially the Human Fusion aspect (Izuku even wonders at one part if they even remember that he can fuse with inanimate matter). He's gotten a bit better about it, but it still flares up from time to time, to the point that when Mina and Kirishima want to see him fuse with Ochako and Katsuki and Mina asks to fuse with him, he seems honestly surprised that they're interested.
  • What the Hell, Hero?: Katsuki really gets on Izuku's case for taking all the damage that Izuchako took when she used One For All onto himself, leaving Ochako completely unharmed when they defused and Izuku with the busted arm and even nausea from Ochako's Quirk. All Might shares the sentiment, pointing out that while the idea was noble, doing the same in a real-life combat scenario could lead to him being completely incapacitated and force his teammate to defend him.
  • The Worf Effect: Other characters are often subjected to this to showcase how powerful Human Fusions are. For example:
    • The Sludge Villain restrains Katsuki and wards off Izuku, like in canon. Katzuku, meanwhile, easily blows him apart with one explosion.
    • Izuku and Momo were on the losing end of the Heroes vs. Villains exercise against Shoto and Tenya, two of the strongest students in Class 1-A. When they merge into Moku, however, the tables turn immediately and she curb-stomps both of them in quick succession.
    • Tsuzuru restrains Kurogiri, Shigaraki, and Nomu easily before rescuing Aizawa from their clutches. The defeat was so humiliating for Shigaraki that he Rage Quit his plan not long afterwards.
  • Zerg Rush: The League of Villains during the USJ incident. As the students note, most of them are two-bit thugs that even they can handle; however, there's so many of them that it's actively preventing Class 1-A from reuniting at the entrance. Those at the entrance can't leave to help either, as they're being attacked by villains too while also trying protect their injured teachers.

Alternative Title(s): Deku The Fusion Hero


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