History Fanfic / DekiruTheFusionHero

What if Izuku's Quirk was a combination of [[Franchise/Ben10 Kevin Levin's Osmosian ability]] and the Fusions from ''Anime/DragonBallZ'' and ''WesternAnimation/StevenUniverse'')? Well this is that fic, Izuku's fussions amplify and alter the abilities of his partner, What If Ochako could control what she floated? What if Momo could ''become'' any material? Find out, here.

NotSoDifferentRemark: Nedzu comments on how Todoroki's attitude toward Izuku reminds him of "another combative future hero who once fought at UA". And Mt. Lady unknowingly echoes that statement, commenting "Like father, like son" in regards toward Todoroki's attitude.

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 [[Franchise/Ben10 Kevin Levin's Osmosian ability]] and the Fusions from ''Anime/DragonBallZ'' and ''WesternAnimation/StevenUniverse'')?

** 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.

* JumpedAtTheCall: 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.

** [[spoiler: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 down Nomu.]]

* HeterosexualLifePartners: 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.

* VitriolicBestBuds:
** AdaptationalNiceGuy he may be, but this is still [[JerkWithAHeartOfGold 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.

* AdaptationRelationshipOverhaul: Any animosity Deku and Bakugo have in canon is nonexistent in this fic, and they are bonafide friends who support one another.

** 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, reaching [[NotHyperbole room-chilling]] anger when Izuku says "What do you want me to do, only use half of my Quirk?"

* CastFromStamina: 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 [[HourOfPower transformation time]] faster than is normal. [[spoiler: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'']].

** 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, he ran the risk of exposing All Might's secret due to its MentalFusion nature. [[spoiler: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]].

* DestructiveSavior: Zig-zagged. 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.

** 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 ExposedToTheElements, which is a problem in the Heroes vs. Villains exercise, where he's paired off with Momo against [[AnIcePerson Shoto]]. All Might caught this but decided to let him discover it himself so that it'd be a learning experience for him.

* DynamicEntry: How Izuku and one of his Fusions saves Aizawa from Shigaraki during the USJ attack.

** Katsuki and Izuku are so glued at the hip neither notice the [[OhCrap memory sharing]] aspect of Fusion until after Ochako knows about All-Might. They're only able to confirm it by checking to see what each other had for breakfast.

** [[spoiler:Three-person fusions are more problematic, since while Tsuzuru (Izuku, Tsuyu, Minoru) is a girl, Katzuchako (Katsuki, Izuku, Ochako) is a boy.]]

** 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 supply a good defense for his mentor.
* JumpedAtTheCall: Mina is actually really unexpected for Izuku, as she's the first person to actually 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.

** 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 [[spoiler:when Izoru fuses with Tsuyu, she learns about All-Might's SecretIdentity]].

* NotQuiteDead: The Anti-All Might Nomu has just been dumped into USJ's lake [[CementShoes 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.

*** Izuku, Minoru and Tsuyu when Kurogiri overhears Minoru mentioning where the Nomu was, which allows him to retrieve him.
*** Then a MassOhCrap version when the Nomu who looks like he had drowned in the lake turns out to still be alive.

* PunchedAcrossTheRoom: What happens to Shigaraki after he tries messing with one of Izuku's Fusions.

* TongueTrauma: What happens when [[spoiler:Tsuzuru]] takes a long fall and tries to catch herself with her OverlyLongTongue while remembering that Tsuyu's tongue isn't sticky enough to catch - and jerking to a sudden halt when it does catch thanks to [[spoiler:Izoru's added stickiness to the fusion's Quirk]].

* TemptingFate:
** 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 [[spoiler: their triple-fusion with Tsuyu, Tsuzuru, dropped him into the lake glued to a mass of steel]]. Unfortunately, Kurogiri hears him and makes a [[ThinkingUpPortals portal]] to get him out.

** AdaptationalNiceGuy he may be, but this is still [[JerkWithAHeartOfGold 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 minor friendship in the time before the semester begins.
** 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.

* SuperpowerLottery: 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[[spoiler:(s)]]. Combined with One for All, it's almost a guarantee that he'll one day be the strongest hero in the world, bar none.

** Human Fusion is treated like this. While it isn't explicitly ''forbidden'', it's 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, he ran the risk of exposing All Might's secret due to its MentalFusion nature. [[spoiler: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]].

* CripplingOverspecialization: {{Discussed|Trope}} 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. Isuku himself is aware of this, and makes it a point to use Human Fusion only as a last resort.

** 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.

* CripplingOverspecialization: {{Discussed|Trope}} 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.

** [[spoiler:Multi-person fusions are even worse than regular Human Fusion. While the fusions are more powerful, they]] drain even more stamina [[spoiler: 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 [[spoiler: 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]].

** 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.

* ElementalShapeshifter: Thanks to Momo's Quirk, their fusion is able to transform into any material that they can think of, no outside material required.

** Just like in canon, one of the top students of Class 1-A eats a big helping of HumblePie after losing the Heroes vs. Villains exercise. Though, in this case, it's not Katsuki ([[AdaptationalNiceGuy whose ego is much more manageable compared to canon]]), but instead [[spoiler:Shoto]], who is defeated by [[spoiler:the fusion of Izuku and Momo]]. [[spoiler:Shoto]] was even teamed with Tenya, like Katsuki was.
* InstantSedation: Tsuku's paralyzing mucus can take effect almost instantly when she uses her tongue to apply it. The mucus from her skin is slower-acting.

* TongueTrauma: What happens when [[spoiler:Tsuzuru]] takes a long fall and tries to catch herself with her OverlyLongTongue while remembering that Tsuyu's tongue isn't sticky enough to catch - and jerking to a sudden halt when it does catch thanks to [[spoiler:Minoru's added stickiness to the fusion's Quirk]].

** 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, reaching [[NotHyperbole room-chilling]] anger when Izuku says "What do you want me to, only use half of my Quirk?"

* SoreLoser: [[spoiler:After his plan fails on every level, Shigaraki decides bail with Kurogiri... but not before leaving Nomu behind to kill everybody in the USJ]].

** 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 pulls them into himself), and it requires two people to do human fusion. It also has a MentalFusion 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.

* ArmorPiercingResponse: In respone to Todoroki insulting Human Fusion, Izuku asks "What do you want me to, only use half of my Quirk?".

** 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, reaching [[NotHyperbole room-chilling]] anger when Izuku says "why would I limit myself to only half my Quirk?"

** 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.

* AdaptationalRelationshipOverhaul: Any animosity Deku and Bakugo have in canon is nonexistent in this fic, and they are bonafide friends who support one another.

* StealthHiBye: Tsuyu pulls this on Mina and Kirishima on their way to Dagobah Beach on chapter 13. They [[DelayedRection need a moment]] to realize that Tsuyu wasn't there a second before.

** [[spoiler: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.

** 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.

** [[spoiler: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]].

** [[spoiler:Triple-fusions]] are ridiculously powerful but exhaust Izuku much faster than normal.