Adaptational Badass / Fan Fiction

Fan Fic writers love to make their favorite characters far more badass when they're the ones writing them.

Backyard Sports

Batman
  • Stephanie Brown in Macushla. After her father is killed for unknown reasons by the League of Shadows, she's taken to serve under Talia al Ghul. She's a master assassin before she's 18 years old and becomes Damian Wayne's bodyguard/Morality Pet. (After Talia fakes Stephanie's death and sends her away because she and Damian were too close, he leaves the League and asks to join Dick Grayson of his own will).

The Black Cauldron

Bleach
  • A Protector's Pride: Ichigo starts the Soul Society arc with access to his Hollow powers. All the the good guys in general are a lot smarter and pragmatic than in canon, especially Chad and Orihime, who are not useless.

Calvin and Hobbes

Code Geass
  • In the original anime, Lelouch had plenty of courage and was good with a gun, but him being out of shape was a Running Gag and he didn't stand a chance in a fistfight. In Code Geass: The Prepared Rebellion, he's much more athletic and quite proficient in martial arts.

Crossover
  • Several background ponies get turned into much more effective fighters in Ace Combat: Equestria Chronicles. Especially those flying in the Mirage squadron.
  • Remember how Yuuno was in Lyrical Nanoha? In Blood That Flows, he's easily as badass as any of the main characters and can hold his own against Gods and Demons just as well as any of the other characters in the story.
  • In the stories written by Crossoverpairinglover on Fanfiction.net, virtually every character gets upgraded to a point they are badasses. Genuine Lockharts, super saiyan-like Sakuras, Apollos who create black holes, etc.
  • Jack in Cave Story Versus IM Meen, to the point where he becomes a Badass Bookworm who literally has the ability to use fucking ZA WARUDO.
  • Children of an Elder God: The three main characters are a bit more heroic and way more badass than their canon counterparts. Shinji pilots his giant robot willingly and gains powers, Asuka becomes a better fighter and gains fire powers, Rei is terrifying...
  • While Shelly De Killer was always a skilled assassin, his combat skills get a huge boost in No More Turnabout, being able to hold his own against the likes of Henry Cooldown and later on, Travis Touchdown, nearly killing the latter had Sylvia not intervened.
  • While Taylor Hebert was already badass in Worm, she ups her badassery by several orders of magnitude in The Last Daughter, where she is actually Kryptonian. Virtually every fight she's in is a Curb-Stomp Battle in her favor, and she actually manages to kill Behemoth.
  • The main Digimon characters from Digimon Fusion Kai are given the ability to become beings that look like Super Saiyans.
  • While in Mahou Sensei Negima!, Ayaka was a self-taught martial artist with her own personal form, she was only Asuna's equal up until Can't Catch Up took effect. In Equal And Opposite Attraction, she becomes a front-line fighter who was trained by Setsuna.
  • Arctic Rim does this to Anna and Elsa, the former becoming a Crazy Awesome hilarious badass and Elsa becoming a bona fide Badass In Charge. The Precursors are also a lot more proactive here than in Pacific Rim, with one in particular (the story's Big Bad) who borders on Magnificent Bastard.
  • The Games We Play turns Jaune from Butt Monkey to legitimate badass via the mechanics of The Gamer. In canon, he's far, far behind any of the other main cast. Here, he's able to, among others, beat Weiss, turn a Delaying Action against Penny into a win, and fight Pyrrha to a draw. And he hasn't even gotten into Beacon yet!
  • The Heroes Of Time does this to the Hanna-Barbera universe. Most of the characters in the shared world are rather peaceful people, and never mean harm. But when The Heartless invade and start swallowing worlds, it's time to take up Keyblades and fight.
  • In Hottie 3: The Best Fan Fic in the World, the Fan Sequel to the novel Burning Ambition by Jonathan Bernstein, Hottie co-pilots her own Tengen Toppa Gurren Lagann-inspired Gunman. The other co-pilot is Squirrel Girl hersel. She later gains three Super Modes, each more powerful than the last. The most powerful Super Mode, Super Hottie Goddess, makes her a Physical God.
  • Just An Unorthodox Thief takes Risei, an intelligent enough character in canon, and tuns him into Tokiomi's Hypercompetent Sidekick.
  • In Magical Pony Lyrical Twilight, the Nachtwal received a massive power and skill boost, including changing its canonical Clipped Wing Angel into a proper One-Winged Angel.
  • In Castlevania: Chronicles of Sorrow, the Chronomage was just a quickly defeated obstacle. In My Little Castlevania, he's an active villain, able to fight Aeon one-on-one repeatedly, and wins several times.
  • No Gods, Only Guns, Ambassador Donnel Udina becomes a full-on Guile Hero, humiliating the batarian ambassador in front of the Council, and also possessing an eyepatch and cybernetic hand. Doctor Michel, usually a Distressed Damsel, takes a buzz-axe to the goons threatening her. And Niftu Cal, a volus who claimed to be a biotic god while doped out on drugs, proves himself to be a very powerful biotic who can back up his claims.
  • In No Hoper, Light Yagami, a Non-Action Big Bad in canon, is now a vampire with powers over the elements, a Hunter of His Own Kind, and a Master Swordsman.
  • Both Shinji and Kaworu in Shinji And Warhammer 40 K go from canon runty, troubled kids, to nigh-Physical God Magnificent Bastards who excel at Xanatos Speed Chess.
  • While Naruto Uzumaki has grown into a powerful badass in his own manga, Shinobi Of The High Seas turns him into a Showy Invincible Hero that manages to go through the Grand Line and ultimately fight Akoji, one of the most powerful admirals in One Piece, to a standstill.
  • Storms Overhead has Louise and Henrietta get an upgrade; the former packs new Void element spells that can defy the laws of physics, including matter destruction (or at least, appears to be so) while the latter commands her nation with equivalents of modern day policies. Seeing that they're both mentored by a scientist/scholar, it was bound to happen.
  • Thousand Shinji: In the original Evangelion show Shinji was a wimp, Rei was properly trained but she was weak, and Asuka was a good warrior but she got her butt kicked constantly. In this crossover with Warhammer 40,000, the three pilots gain huge powers and take several levels in badass: Shinji becomes a sorcerer with psychic powers, Asuka a berserker super-soldier and Rei a plaguemaster.
  • Time Lords and Terror, a Friendship is Magic and Doctor Who crossover, re-imagines the events of the G1 movie as a Cosmic Horror Story. Instead of kid-friendly villains, Hydia, Draggle and Reeka are now The Fair Folk-inspired aliens. They now beat ponies bloody and harvest their life force to awaken the S'Muz (aka the Smooze) an Omnicidal Maniac, driven by hate, Eldritch Abomination that causes a wave of madness by its mere unsealing, that wants nothing more than destruction of all universes.
  • In Unfamiliar, almost every canon character from The Familiar of Zero (but especially Princess Henrietta) gets a massive competence boost and a power upgrade. Considering that they're expected to cope with One-Man Army Alex Mercer, this is perfectly understandable.
  • In Justice Society of Japan while Mordred has a relationship to Morgaine Le Fey similar to how he was depicted in Justice League, in this continuity, the preteen is now less of a Royal Brat and more of a Loyal Implacable Man. Also, Shirley Fenette has been upgraded from a schoolgirl to one of the main heroes.
  • Last Child of Krypton does this to plenty of characters, but first and foremost is Shinji Ikari, who turns out to be half-Kryptonian in the story. Later examples also include Asuka, Toji, Rei, Kaji, and Naoko Akagi.
  • Superwomen of Eva 2: Lone Heir of Krypton: Asuka was the best Humongous Mecha pilot in the original story, but she was still a physically fit thirteen-years-old human. In this story she has kryptonian DNA with all it entails: she is super-strong, faster than a speeding bullet, nearly invulnerable... and she can fight giant Eldritch Abomination with her bare fists.
  • Many canon characters from YuYuGiDigiMoon have given power ups: such as the Digimon Tamers receiving beast powers base on the Four Chinese Symbols, and the Sailor Senshi receiving the mysterious Valkyrie forms.
  • Justice League of Equestria: Deathstroke has always been a skilled fighter in The DCU, but here he manages to get the drop on Rainbow Dash (this universe's equivalent to Superman) in their first encounter, and then manages to almost defeat her again during their fight in Cloudsdale.
  • Child of the Storm has a number of these:
    • Sean Cassidy goes from C-List X-Man (B-List on a good day), famous for screaming loudly and (somehow) flying, to a deadly spy with decades of experience and, thanks to a Noodle Incident, the physique of a man in his prime. And as he demonstrates on HYDRA troops, his abilities go far beyond simple screaming and he most definitely knows how to use them.
    • The Winter Soldier progresses from street level nightmare and Darth Vader Clone to the terror of the entire Western World, an immortal wraith-like figure and One-Man Army who induces pants crapping levels of terror from just about anyone who hears of the possibility that he might be around. And he backs up the hype too: he's one shotted a former Captain Britain, for instance. In one of his rare on-screen appearances, he's killed James Bond with minimal effort. And he killed Kennedy. Loki calls him possibly the most dangerous assassin in the Nine Realms, and it's kinda hard to argue with the guy.
      • In chapter 60 he shows what he's really capable of by ambushing Steve, Natasha and Clint and having them dead to rights.
    • Harry packs more magical power than in canon, growing into a fully fledged Guile Hero who actually plans ahead to an extent, while remaining a master of the Indy Ploy. He's also a lot more confident, to the point where he's more than willing to stand up to gods and monsters alike with absolutely no fear. Plus he's got Wanda's blessing at his back, which means that he's even more magnetic to potential hero types than before. And all of that aside, he's a Prince of Asgard whose powers are beginning to come through.
  • On Core Line, this is the essential fate of anybody who enters the post-multiversal Reality Bleed World of Badass of the setting. They all have to become sharp, or risk dying (at worst). And as such, whenever any two characters of two differing fandoms clash (any two), it's up in the air who will win (if they are not cut down mid-fight by a Badass Bystander who's had enough).
  • The Good The Bad And The Demon has April O'Neil and her best friend, Hitomi Tono. In the former's case, using more of her psychic abilities ever since she found she's half-human, half-Kraang, while the latter has learned to fight with April's help.
  • Weiss Reacts:
    • Cardin went from vaguely wimpy Jerk Jock to Bad Ass Gentle Giant who is considered The Dreaded.
    • Blake now has the Gurren Lagann at her beck and call. She also uses Spiral Energy in addition to Aura.
    • Jaune is a lot less wimpy and a lot more Genre Savvy, capable of holding his own in a fight. Also, Nora now utilizes Confusion Fu and, in some chapters, borrows her mother's railgun.
    • Tukson, who was killed in the first two minutes of Volume Two, is a master Huntsman and martial artist capable of taking on Team RWBY by himself here. Not only that, but he doesn't need weapons; he's a Bare-Fisted Monk who uses Ki Attacks.
    • Over in Lucina Reacts, Kellam is turned into The Ace, who matches the canonical Ace Cordelia for competence. This is a downplayed example in that Kellam was already a canonical Bad Ass, but much more understated and less focused on.
    • In Homura Reacts, Hitomi is turned from a rather average Ojou to a Lady of War capable of taking on Sayaka and Kyoko on a two-versus-one fight and win with her bare fists.
  • The Bridge: Kaizer Ghidorah became an expert at close combat in addition to his already overwhelming strength and energy attacks.
  • Persona EG: Flash Sentry, as the main character, is a Wild Card, is very good at playing Guitar, seems to be a Chick Magnet, and has gotten good at swinging a battle axe around. Not bad for a fairly minor character from the Equestria Girls movies.
  • Paper Mario X gives Malon archery skills and magic music power. The bosses are also much tougher to make the fights more interesting due to how many more characters they're fighting at once.
  • A RWBY Zanpakuto:
    • Ichigo Kurosaki has four zanpakutos, the weapons of Team RWBY, and access to his Hollow, Quincy, and Fullbringer powers during the Soul Society arc.
    • Uryuu Ishida is much more creative in applying his powers, and manages to kill Mayuri in a way that gains him his knowledge.
    • Orihime Inoue is more willing to fight, and gains a limited teleportation.
    • Chad actively trains with Yoruichi and becomes powerful enough to actually challenge Arrancars.
    • Rukia becomes a Visored and gains her Bankai early.
    • Tatsuki becomes a Fullbringer and becomes powerful enough to challenge Arrancars. She's also the one who defeats Tsukishima.
    • A Hollow's Healing Factor can repair damage to internal organs, while in canon it could not.
    • Ulquiorra has an Adaptive Ability.
    • Aizen has a Sword Beam attack, actually uses his Bankai, and his final battle with Ichigo is much more impressive.
  • While in canon, Foquet the Crumbling Dirt was skilled at making giant golems and not much else, in Star Wars Episode I: The Familiar of Zero she's a badass Square Class earth mage capable of matching a Sith in a sword fight. Her claim that fighting her "is to fight the earth itself" isn't an empty boast either as she can strengthen her body, create pits of quicksand, and conjure nigh indestructible adamantine golems. If Guiche's reaction is anything to go by, she's the earth mage equivalent of Karin the Heavy-Wind.

Death Note

Digimon

The Familiar of Zero
  • Canonically, Saito was just a regular guy until he was chosen as Louise's familiar. However, in Zero no Tsukaima: Saito the Onmyoji, he was already a fully-accredited mage, and being summoned to Halkegenia only made his powers greater.

Final Fantasy VII
  • Kunsel is a normal Second Class with being a well informed and vaguely gossipy Mr. Exposition as his distinguishing trait and doesn't stand out in a company with the likes of Sephiroth and Zack Fair. In the The Fifth Act, he is shown to match Zack in skill when given the motivation and to be far more perceptive and knowledgeable than people realize. Kunsel is upgraded to being a powerful Knowledge Broker having a vast information network, being everyone's go to guy for information and in the Omakes, being better informed than the Turks.

Harry Potter
  • Harry Potter and the Methods of Rationality:
    • Severus Snape has been spiking Lord Voldemort's father's grave with every dangerous drug and poison known to wizardkind (and LSD—because it might affect him), as well as every other grave in the cemetery on account of Voldemort might have moved the gravestone, and the graves of every other ancestor of Voldemort's that he and Dumbledore could track down, just in case. Too bad Voldemort foresaw this contingency and, since he couldn't move his father's bones if he wants the resurrection spell to work, moved the entire rest of the cemetery to an entirely different location and memory-charmed the local Muggles.
    • Harry Potter, in so many ways. Here's his following plan:
    • Draco Malfoy went from The Bully to Manipulative Bastard, The Starscream to Harry, and scion of a long, proud line of Men Behind the Man.
    • Quirrell in canon is a simpering stutterer who's a host to Voldemort. Word of God says this Quirrell is possessed by Voldemort, which now makes him an Evil Mentor to Harry, a sixth-dan in an unspecified martial art, and he horcruxed the pioneer probe! Oh, and then he went and tricked Harry into breaking Bellatrix Lestrange out of Azkaban.
    • Blaise Zabini went from Draco's crony to a quintupple agent in a war with only three sides.
  • Cruciamentum Eternus includes Lucius Malfoy during the time period of the last book. In the canon he was broken, pathetic, weak, and didn't fight Voldemort until it was safe to (and Narcissa pushed him). In this story, Draco's murder has him secretly murdering Death Eaters from almost the moment he's released from Azkaban, while still feigning allegiance to Voldemort's side, with the ultimate plan of killing Voldemort himself. If nothing else that requires at least an epic feat of Occlumency and a strength of will he never shows in the books.

Jackie Chan Adventures

Kamen Rider Fourze
  • In Horseshoes and Hand Grenades, nearly every single character who ever appeared in Kamen Rider Fourze have gone into fighting mode. This ranges from Yuki Jojima using her Hayabusa Plushie as a boxing glove, Chuta Ohsugi fighting off his former love interest, Sarina Sonada and minor characters like the ones in the Amanogawa High Glee Club consist of a sword wielder, a samurai and a ninja.

Kingdom Hearts
  • The Princesses of Heart in Stygian Solace. Snow White can hold her dying world together with sheer force of will despite being the only human survivor and all of them together can force Id and Maleficent through a Heart Beat-Down and their powerful light magic. Kairi unintentionally can create life as seen with Yami.

The Legend of Korra
  • While Korra was undoubtedly badass in canon, she is even more so in The Saga Of Avatar Korra, accomplishing or gaining abilities sooner than her canon counterpart due to being raised and put through a Training from Hell regiment by the Red Lotus for fourteen years, and delivering Curb Stomp Battles to characters who were more difficult for her to defeat in canon, such as Unalaq, Desna, Eska, and Kuvira.

Love Hina
  • Contract Labor: In direct contrast to the Extreme Doormat he was in canon, Keitaro actually has some backbone and is far more willing to stand up to and for the Hinata's residents, even managing to defeat Motoko in an honor duel.

Lyrical Nanoha
  • Game Theory (Fan Fic):
    • The Jewel Seeds get a serious upgrade in their power and threat level. As the author explains:
    Aleph: Nanoha showed us that the Monsters of the Week could be a backdrop to the real meat of the plot, the character interaction, but then Madoka came along and showed us that the Monsters can still be legitimately, vividly scary. And Game Theory is very much a post-Madoka story, with the harsher rules and the scarier monsters and so on.
    • Pretty much all the characters over the age of about sixteen or so get a significant competence boost. They aren't any more powerfulnote , but they use what they have much more effectively because they employ proper tactics, especially Precia (since the entire premise of the story is that she's only slightly insane instead of full-blown bonkers). The Wolkenritter in particular have received a major upgrade in skill, showing the experience and tactical acumen that would be expected of centuries old combat constructs.

Mai-HiME
  • Yukino in Perfection Is Overrated. In the original series, her Child was only good for surveillance, and left her easily defeated by Shizuru. In this fic, she realizes that while she's not the best in a straight-up fight, she can use her powers to tip the balance of power in her favor at crucial moments, such as when she incapacitates Shiho, enabling Mai to win her battle without Yuuichi dying, and when she, in the final battle, uses her Child's abilities to immobilize one of the last remaining SUEs' Child long enough for Natsuki to finish her off.

Marvel Universe
  • This trope is a staple for the villains of Ultimate Sleepwalker: The New Dreams and Ultimate Spider Woman: Change With The Light. Characters like 8-Ball, the Brothers Grimm, the Chain Gang and Jack O'Lantern were all C-lister villains, at best, in the original comics. In the Earth-2706 verse, though, they're exceptionally deadly threats, forming the focus of the Fics.

My Little Pony
  • Pony POV Series:
    • Mimic is said by Princess Luna to have been the first, and only, mortal pony to injure Discord, by kicking him in the face at supersonic speeds until she knocked his tooth out. He killed her afterwards, but still. Starsong probably also counts, managing to fend off Discord's brother Anarchy for a considerable time.
    • While Princess Cadence turned out to be pretty badass in canon, the version of her in this series was able to take on an avatar of Discord's father Havoc and not only survive, but it's implied that she won.
    • There's also the CMC, who manage to be Badass Adorable in this universe, Minuette and Twinkle Shine, who really get to show off their Gifted Unicorn credentials, Shining Armor, who saved the world from an Imagination Demon, and Trixie who becomes the Sixth Ranger and grows to be able to fight Twilight on fairly even standing. Honestly it's easier to count the characters that don't count.
  • Rainbooms and Royalty has Zecora, while still being the mentor to the Mane Six like in canon, also proved personally fantastic repeatedly over the course of the series, with such highlights as saving Rainbow Dash from the Shadowbolts, fighting Nightmare Moon one-on-one, and saving Dinky, Pipsqueak, and Alula from King Sombra's bushwoolie Mooks.
  • Xenophilia turns Lyra Heartstrings into a grandmaster of the Still Way, the only Unicorn-exclusive martial art. She's described by Rainbow Dash as "probably one of the five or six most dangerous ponies in Equestria, even counting the Princesses," and the only pony in town other than Twilight who could beat her in a serious fight. Chapter 9 reveals her to be an auxiliary Royal Guard, and we also see her in action.
    Lero: Wow. I had no idea. She's always been really friendly to me.
    Rainbow Dash: [giggling] Yeah, I’ve heard that about her. Total sweetheart, you’d never guess that she could kill you in half a second from, like, three hundred bodylengths away.
  • Rarity is slowly heading in this direction within the Triptych Continuum, and it comes from recognizing her own limitations. She has strictly average field strength, knows no spells for direct offense or defense, her physical abilities are nothing special — and she's been placed in a position where she regularly has to risk her life in direct combat. So how is she dealing with this? Through becoming the single dirtiest fighter anypony's ever seen. Take a telekinetic with exceptionally fine directional control who regularly carries sewing needles with her, then pray she doesn't have a straight shot at your eyes. And in physical combat, she'll go for joints, sensory organs, vulnerable spots, and everything else offered without caring about dignity or the pain of the other party, because all that pales in significance to her goal of coming out alive. Compared to the others, she may not bring much to bear — but what she does have is targeted with terrifying efficiency.

Naruto
  • In Vapors because she was found by the Third Hokage and adopted into the Uzumaki Clan as well as studying under Anko, Karin here is capable of holding her own with Sasuke in combat and is often paired with him on missions.
    • In canon Konan got caught by Jiraiya, acted as support during Pain’s attack on Konoha, and got killed by Tobi. Here she demonstrates exactly why she’s The Dragon.
  • In Reverse Kaguya is a joke, an Anti-Climax Boss that was defeated by Naruto’s Reverse Harem Jutsu. Here, Kaguya is the Hero Killer and caused the extinction of the human race and Kurama’s plan boils down to preventing her from awakening.

Neon Genesis Evangelion
  • Evangelion 303: Several characters are more badass than their canon counterparts:
    • Shinji is an adult, seasoned soldier in contrast to his untrained teen pilot canon self.
    • Touji, Hikari and Kensuke are jet fighter pilots rather than average teenagers.
  • Neon Genesis Evangelion: Genocide turned Asuka into a greater badass than her canon self. After recovering from her breakdown, she kills most of giant alien monsters that try to mess with her.
  • In Nobody Dies Kei Ayanami was originally just another one of The Ree with Bond Villain Stupidity as her Quirk. And then The Kei-Files came out, and she was changed into a Manipulative Woobiefied Badass girl with Adorkable and Fragile traits, making her one of the most beloved original characters of the fic.

One Piece

Oreimo
  • In canon, Kousaka Kyousuke is the type of person who lets his sister walk all over him. Contrast this to My Life Can't Lose Its Normality where he (as well as Ayase, Akagi, and Miura) are a team of martial-arts mastering, Yakuza-killing vigilantes who pull off stunts normally reserved for paramilitary organizations and special operatives.

Pokémon
  • In canon, Ash Ketchum is a rather bumbling, childish, and well...stupid, trainer. In The Chosen One's Journey, all that is replaced with maturity, responsibility, discipline, and pure badass.
  • Due to the result of a Peggy Sue plot, Ashes of the Past has pretty much everyone that Ash has come into contact with become a bona-fide badass. This ranges from Ash actively pursuing his Aura Guardian training and fighting Pokémon with his bare-hands, to Charizard learning the Poké-equivalent of a tactical nuke, to Squirtle (as a now-Kamina expy) breaking the laws of physics on a regular basis.
  • Traveler does this pretty much across the board. Of note is Ash himself, who goes from headstrong and clueless in the anime to a more calm and collected battler who makes it all the way to the finals of his first Pokemon League, and shortly thereafter accepts a position as an Elite Four trainee.
    • More than anyone though, the biggest jumps in badass come from the legendaries. Rather than Olympus Mons that are powerful but can be beaten and even captured by the right strategy, or even just a strong enough opponent, in Traveler, the legendaries are just that, legends: uncontrollable forces of nature that can impact whole nations by their mere presence, and whose full power can permanently change the shape of the world.

Ranma ˝

RWBY
  • RWBY Reckoning takes the normally bumbling Jaune Arc, a guy who is nothing like his legendary ancestors, and makes him able to build a functioning time bomb with approximately 18 flares, some duct tape, and some scraps. And it's powerful enough to shred the stomach of a very large Grimm.
  • The Commission takes the formidable, but still in training, girls of Team RWBY and makes them The Dreaded. They're the leaders of each of their groups, all acquired via hostile takeovers, and are engaged in their own conspiracy with such ruthlessness and efficiency that scares the original show's vilains. Heck, those villains appear in this fic as the girls' subordinates.

Sailor Moon
  • Sailor Moon: Legends of Lightstorm:
    • Sailor Moon now fights primarily with sonic screams powerful enough to annihilate buildings, her energy disk can slice through almost anything, and her physical strength is great enough to punch through rocket-proof armor.
    • Sailor Mercury impales things on gigantic ice spears and can stand up to the toughest of Negaverse drones single-handedly.
    • Tuxedo Mask has fighting skills that rival Lightstorm's can cut through virtually any substance with his razor-roses, hits hard enough to knock gigantic drones off their feet, and can withstand explosions strong enough to shred drone armor.

Sonic the Hedgehog
  • Sonic X: Dark Chaos:
    • Tails goes from being a weak, shy Gadgeteer Genius into a Magnificent Bastard captain who gains a Lovecraftian Superpower and ends up saving the entire universe from an Eldritch Abomination at the cost of his own life.
    • Cream stays with Sonic and friends to the end, even after seeing things that would make most adults break down. In Episode 66, she and her chao Cheese ends up beating Astorath the Prince of Darkness on her own.
    • Cosmo saves several planets before becoming acting captain of the Blue Typhoon, and she is also appointed leader of the Metarex during the final battle. And in the rewrite, when Astorath and Beelzebub land on her ship, she runs out onto the flight deck with Venus' demon scythe and rips them a new one.
    • Chris Thorndyke goes from being a whiny, dependent brat to a Genius Bruiser, pulls off a Big Damn Heroes and unleashes Death from Above with the Typhoon in the rewrite of Episode 69, and later on fights Beelzebub and Astorath alongside Cosmo during the final battle.

Soul Eater
  • Soul Eater: Troubled Souls: An increasing number of canon characters show more skill or competency than their original counterparts, which is saying something. They are even gifted more techniques and moves than normal, especially those who lacked them. Here are some specific examples:
    • This fic plays up Tsubaki’s abilities as a ninja or assassin. She also seems to be a bit more resourceful.
    • In canon, Ox has a pretty limited repertoire of techniques and moves. Here, he has plenty to spare, up to and including a Soul Resonance between him and Harvar.
    • Crona receives stronger forms, learns Soul Resonance, can fight Medusa on equal or better footing, overcomes Mad Blood, and is saner. Oh, also, "badass" as in kills Medusa permanently!
    • Kim fends off Medusa Gorgon long enough until The Cavalry comes without her Regeneration Magic.
    • The Mizunes, specifically their fully combined form. In the original manga, that form of Mizuna is only seen in a fanservice cat fight with Blair. Here, this is the sisters' most powerful form, and they absolutely destroy Caius and Tsuji in the Cobra Island arc.

Super Mario Bros.

Super Why!

Sword Art Online
  • In The Kirita Chronicles Kirita, the Gender Flipped version of Kirito, is more capable of being able to defend herself in the real world than he could. After quitting Kendo, she took up karate classes and is capable of delivering curb stomp battles to bullies and her fellow karate students. In canon, it is assumed Kirito focused solely on computers and video games. After being trapped in the video game, Kirita trains even harder to become stronger because she believes players will consider her vulnerable if they find out she is a female player.

Tengen Toppa Gurren Lagann

Touhou
  • Rumia is lowest of the low in Gensokyo's hierarchy, weak and with a useless power. It's widely speculated however that she possesses a Superpowered Evil Side, meaning most fan works featuring her give her an appropriate power boost, though the degree of the boost varies vastly; Imperfect Metamorphosis for example makes her into a Walking Wasteland and a Fallen Angel, whereas in Touhou Nekokayou she's slightly more powerful but still comic relief.
  • Cirno, another canonically weak boss who is a fan favorite due to Awesome Ego, also gets this treatment quite often whenever she's not the Memetic Loser instead. Does this look like a stage 2 boss to you?
  • Imperfect Metamorphosis:
    • Kotohime was a generally ineffectual and totally delusional combatant in her original appearance. In this Fic, she's graduated to the rank of Beleaguered Assistant to Yukari herself, running Gensokyo's first police force, and at one point she delivers a beatdown to Marisa Kirisame for disintegrating one of her officers (she got better).
    • Yuuka Kazami in canon is certainly powerful and has aspects of The Dreaded, but there are plenty of characters who could take her in a fight. Yuuka in IM is the most feared being in Gensokyo's history, a nightmare who no-one dares confront directly, and who shrugs off all the attacks leveled at her by Yukari and her team she assembled specifically to kill Yuuka, in the process revealing her nature as an Outer God.
  • Mokou is already an immortal powerhouse and EX-Boss. Touhou Ibunshu in addition has her possess the powers of a Physical God, giving her the strength to go toe-to-toe with Yukari after creating an army of thousands of kashoyo.
  • Maiden's Illusionary Funeral takes Yukari and Ran, already ancient sages with near-unsurpassed abilities, and makes them both The Juggernaut who cleave through groups of specialist youkai hunters without a scratch. This in turn makes Yuyuko one as well, given she nearly killed Yukari while still trying to restrain her powers.

Worldwar
  • In Worldwar: War of Equals, all of South America, Central America, and Eastern Europe put up much more of a fight than they did in the source material. Human tanks qualify as well. In the original novels, even the best Human tanks of the 1940s could easily be destroyed by a single Landcruiser. Thanks to tank technology advancing in the last couple of decades, our tanks are either equal to or superior to their Landcruisers.

Worm
  • Quicken: In the original story, Emma was a powerless, cowardly girl. Here she’s a regenerator super-human capable of detecting other super-humans and stealing their powers and memories after killing them, and prone to go berserker.

Young Justice
  • In Young Justice Titans, the Scarecrow gets a serious badass bump. Thanks to becoming a member of the Church of Blood, he's given supernatural powers, and is hinted at being essentially a real living scarecrow now, with impossible flexibility, his Sythe that he pulls out of his mouth, and fear gas in both Gas and solid forms. He's even able to fight a team with powers far beyond him (including a Green Lantern). He's also almost unkillable too.

http://tvtropes.org/pmwiki/pmwiki.php/AdaptationalBadass/Fanfiction