History Fanfic / DekiruTheFusionHero

* AdaptationalNiceGuy: 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 OnlyFriend for a long time. While he can still be a bit of a {{jerkass}} in the present, he comes across more as a JerkWithAHeartOfGold to Izuku and, later, Ochako.

** 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.

** 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.

** 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.

* 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''. Fusing into Katzuchako is even worse, with Izuku, Katsuki and Ochako left exhuasted, dehydrated and with low-blood sugar afterwards]].

* 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. Izuku himself is aware of this, and makes it a point to use Human Fusion only as a last resort.

* CutenessProximity: 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.

** 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 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: 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.

** 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 MegatonPunch with every blow. He can still launch extremely powerful blows, what would normally be considered a MegatonPunch and what would have outright crippled his arms after one use in canon, but it's not the OneHitKO that it normally is.

* DynamicEntry: How [[spoiler: Tsuzuru]] saves Aizawa from Shigaraki during the USJ attack, launching [[spoiler: herself]] down from the facility's roof and hitting the villian square in the face.

* EmbarrassingNickname: Katsuki barely tolerates Izuku calling him "Kacchan", but he absolutely hates when everybody else starts doing it.

** Katsuki and Izuku are so glued at the hip neither notice the [[OhCrap 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.

** 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.
** [[spoiler: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 VitriolicBestBuds. Izuku himself has no issue calling Tsuyu "Tsu" after the fusion, something his canon self still has difficulty doing]].

* ForWantOfANail:
** 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 SuperSpeed. Tenya is instead sent to the landslide zone, in place of Katsuki. [[spoiler: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]].
** [[spoiler: Nomu is ultimately defeated by damaging it enough that its HealingFactor just can't keep up anymore, before All Might even ''arrives'']].
** During the Obstacle Race of the Sports Festival, Todoroki's grudge against Izuku leads to him deliberately blocking the latter of at the Fall with a huge ice wall, and then melting it when Izuku tries to climb over. Seeing Todoroki endanger mutiple people out of pettiness angers Izuku enough that he turns back to help them, leading to him making a new Fusion with Sero, and [[spoiler: Katsuki ultimately winning the race and Izuku coming in second.]]

** 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. The fact that his fusion with Tsuyu is also girl points to Katsuki being right.

* 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.

** 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 Shoto, who is defeated by the fusion of Izuku and Momo. Shoto was even teamed with Tenya, like Katsuki was.

** On top of that, it seems that people who fuse with Izuku adopt some of his personality traits and [[{{Pun}} 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.

* 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, Katsuki and All Might have a collective one when Izuku's first use of One For All at the beach almost obliterates his arm.

* PrideBeforeAFall: 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. [[TranquilFury 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.

* RomanticFusion: Izuchako, the fusion between Izuku and Ochako. Unlike the TropeCodifier [[WesternAnimation/StevenUniverse 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.

* SoreLoser: [[spoiler: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]].

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

* StupidSacrifice: 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 [[ChronicHeroSyndrome 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.

** [[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 on Nomu.]]

** 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, [[spoiler:Class 1-A is even able to hold off Nomu]].

* ZergRush: 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.

** On top of that, it seems that people who fuse with Izuku adopt some of his personality traits and [[JustForPun 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.

* AmazonianBeauty: Tsuku, Tsuyu and Izuku's fusion, is described as being very tall and noticeably muscular.

* AdultFear:
** 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 [[spoiler:Tsuzuru]], because that means the thing that beat him bloody is now chasing after someone who is effectively [[spoiler:three of his students]].

* GodzillaThreshold: [[spoiler: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]].

* 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. Later, Hanta similarly suprises him at how quickly he accepts his offer to fuse, to the point where he didn't even let Izuku finish asking before saying yes.

** 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.
** [[spoiler:Tsuzuru restrains Kurogiri, Shigaraki, and Nomu easily before rescuing Aizawa from their clutches. The defeat was so humiliating for Shigaraki that he RageQuit his plan not long afterwards]].

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.

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

* ChromeChampion: 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 ElementalBaggage.

** 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.