“Something small can have huge ramifications further down the line, exactly. It’s a part of chaos theory.”
— Yagi Toshinori, regarding the Butterfly Effect
The first over-night trip off campus since the training camp was supposed to be a fun break from more intense work back home. But between a bleak introduction to chaos theory, a chilly reception from the locals, and the looming threat of a villain attack, Izuku has too much on his mind to properly enjoy the fresh air. But those worries are a light breeze compared to the hurricane that accompanies what he finds on the outskirts of town.
Or rather, what finds him.
Butterfly
is a My Hero Academia Horror Fan Fic by aconstantstateofbladerunner. The sequel, Moth, is currently ongoing and has its own page.
The main antagonist’s In-Series Nickname will not be given spoiler tags in order to avoid talking in circles around it. Still, it’s best to read the story without prior knowledge for the full dosage of Nightmare Fuel.
This fanfiction provides examples of:
- Act of True Love: Toshinori presents one to Izuku by allowing him to leave his apartment if he truly insists on hunting Butterfly. He accepts that he can't stop the boy and assures him that he'll accept Izuku with open arms if he decides to come back. To his relief, Izuku stays put.
- Adaptational Nice Guy: Mineta doesn't show his perversions in the story and is presented as a pretty decent guy towards his classmates.
- Alas, Poor Villain: It’s hard not to feel bad for Butterfly once you find out that he’s Izuku from an alternate dimension, and all he wants as he dies is his mother's arms.
- An Arm and a Leg: Himiko loses her whole arm after fighting Butterfly.
- And Then What?: Toshinori chews out Aizawa for suggesting that Eri use her Quirk on Butterfly to bring him back to life. Butterfly is a high ranking criminal and serial killer who's caused chaos and trauma for everyone around him. Even if he were brought back to life, he'd be immediately given the death sentence or sent to Tartarus by some god-ordained miracle.
- Ascended Extra: Midnight and Hound Dog play more prominent roles as they take part in helping Izuku with his PTSD.
- Bad Future: Butterfly's original dimension is a world where Izuku gave up hope and never became "The Hero Who Doesn't Give Up". In this reality, he never rushed out to save Bakugou which led to the bully's death by the Sludge Villain. The USJ Attack is a success as many Class 1-A kids are murdered while a good majority, Aizawa included, are captured and robbed of their Quirks by All For One. Iida is slaughtered by Stain since Izuku wasn't around to save him. All Might faces against Wolfram alone and is killed by the rogue villain; his successor Lemillion would later die by the hands of Butterfly thus ending the One For All Legacy. It's also hypothesized that Yuuei was shut down due to the ongoing deaths and bad reputation.
- Battle Couple: Jakku's top heroes Racing Stripes (a Zebra man who can run really quick) and Cheat-A (a country woman who can make instant portals from the spots on her body) are Happily Married and efficient as a superhero duo.
- Big Damn Heroes:
- In Chapter 14, Aoyama alerts Aizawa about Butterfly preparing to strike Izuku which leads to him barging in to protect his student.
- In Chapter 26, Izuku manages to get the jump on Butterfly before he can kill Toshinori.
- During the final battle, just before Butterfly succeeds in replacing Izuku, Eraserhead reaches the fight scene and uses Erasure to destroy the tragic monster.
- Bittersweet Ending: Butterfly is finally killed, but a child and a few Pro-Heroes were killed along the way and the villain is a mutated and warped Izuku from another dimension desperately wanting to return to his pre- villainous life by any means necessary. Everyone is traumatized by the event but none more so then Izuku, who not only nearly died while fighting Butterfly, but is forced to live the rest of his life with his AU counterpart's memories and some of his organs.
- Bully Turned Buddy: Subverted. During a train ride towards his new hiding spot, Izuku runs into some old classmates from Aldera who ask for a photo with him. Izuku obliges but is annoyed to see how they've conveniently forgotten about the torment and ridicule they inflicted on him during their middle school years.
- Butterfly of Doom: Izuku and Toshinori frequently discuss "The Butterfly Effect" and how one change in someone's life can lead to drastic, and sometimes dangerous, changes in the present.
- Cassandra Truth: No one thinks of Izuku as a liar, but many of them have a hard time believing that there's a villain after him. It's revealed that the villain Butterfly has been purposefully gaslighting him to mess with his sanity and he has several Quirks that can keep his existence a secret.
- Cerebus Retcon: Toshinori confesses that he hates his first public appearance with a passion. While many people, Izuku included, remember him bravely saving countless lives, Toshinori can only think of the horror of thousands dying along with the suffering the victims faced throughout the event. He even claims that the people he did save ended up dying afterwards.
- Dark and Troubled Past: Butterfly's backstory. We learn that he's actually Izuku from another universe where he didn't rush to save Bakugou and never became All Might's successor. He ran away before applying to high school and ended up in the clutches of All For One who turned him into a vessel for his many Quirks. At some point, Wolfram challenged All For One which led the Dark King to transfer his Quirk onto Izuku. From there, Izuku began wandering the world trying to survive on his own with countless Quirks that are destroying both his body and sanity.
- Dark Lord on Life Support: Butterfly is only alive due to the sheer amount of Quirks he has, fuelled by his Horror Hunger.
- Dead Alternate Counterpart: In Butterfly's world, all of the students of 1-A, Aizawa, All Might and Mirio are all dead, the only exception being Kirishima. Bakugo was never saved by Midoriya in his timeline, so he drowned in the Slime Villain. Of the confirmed fates, Aoyama, Tsuyu, Kaminari, and Sero, were killed in the USJ attack. Aizawa, Ashido, and Koda, were all kidnapped and had their Quirks stolen by All For One, then executed afterwards. Todoroki was killed in a training exercise with Endeavor when he overexerted himself. Iida was killed by Stain in Hosu during his attempt to get revenge for Tensei. All Might was killed by Wolfram at I-Island. And Mirio was killed by Butterfly. Kirishima was the only lucky one since it was Midoriya rushing to save Bakugo that helped inspire him to go to U.A., meaning he never went to U.A. in that world. Due to Butterfly's presence, everyone begins suffering what they think are nightmares induced by him, but are in truth experiencing the memories of their counterparts final moments.
- Driven to Suicide: The first plan that Butterfly tries to enact on Izuku.
- Due to the Dead: The final chapter features a funeral on behalf of Butterfly which is attended by Izuku, his mother, All Might, Aizawa and Nedzu.
- Emotion Bomb: Another of Butterfly's abilities is that it can trigger a sense of Dread to it's victims causing them to feel paralyzing fear.
- Enemy Mine: Himiko participates in the final gambit against Butterfly by pretending to be Inko as to lower the monster's defenses.
- Evil Counterpart: Butterfly to Izuku.
- Evil Versus Evil: In the other dimension, Wolfram decides to challenge All For One for the title of Number One Villain. It ultimately ends with both of them dying and Butterfly!Izuku inheriting All For One itself.
- Exposition Beam: Played for Drama. During his failed attempt at stealing Izuku's body, Butterfly transfers his memories onto his counterpart. Even after the monster's death, Izuku is now haunted by Butterfly's memories and is existential paranoia about his true identity.
- Feathered Fiend: A pair (actually two; Albatross and Cherub) of Butterfly’s wings has feathers. They’re not well-cared for.
- Fluorescent Footprints: Pathfinder's Quirk allows him to see the trail of any person of his choosing which makes him a great asset for search and rescue missions. Butterfly would later steal his Quirk and use it to track down Izuku.
- For Want Of A Nail: As stated above, Izuku and his dad discuss the Butterfly of Doom concept after reading the classic sci-fi story "A Sound Of Thunder". This trope is played straight as Butterfly is revealed to be Izuku who comes from a universe where he never ran to save Bakugou or inherit One For All.
- Freudian Slip: In the first chapter, Izuku accidentally calls Toshinori "dad". After all the trauma and suffering the two endure mixed with them bonding, Toshinori happily embraces the title.
- Gaslighting: Unintentionally done by the UA staff in most of the first half of the story. Played straight with Butterfly who's been using his Quirks and shady appearance to ruin Izuku's sanity.
- Hero Killer: Butterfly becomes an even greater threat as it starts to attack and even kill several Pro Heroes and sidekicks. It's also implied that he killed Lemillion and several other Pros in his original dimension.
- Hero with Bad Publicity: A lot of locals from Jakku do not have a positive opinion about Yuuei. They find many of them to be arrogant and pampered for all the special treatment they get from the public and hero government. It doesn't help that many hero hopefuls from Jakku are hardly accepted into the prestigious hero academy.
- Heroic BSoD: The start of Izuku's trauma begins when he walks into a Jakku diner to discover the mutilated corpses of the diner's owner and his son. It gets worse for him as the crime scene lead to him developing anxiety attacks and Post-Traumatic Stress Disorder which severely limits his ability to function as a Yuuei student weeks after the incident. Sero and Tooru also get this as they too witness the crime scene but they turn out somewhat better compared to Izuku.
- Horror Hunger: The missing food and dead deer seem to imply this early on.
- I Want My Mommy!: Sometimes, all Izuku wants is his mother. Butterfly, being Izuku from another dimension, shares this trait.
- Kill and Replace: Butterfly's ultimate goal is to have Izuku die in order to replace him and live out his Happily Ever After. His plans on doing so ranged between gaslighting Izuku into committing suicide to outright abducting him and pretending to be him. He ultimately goes for trying to forcibly trade bodies with him.
- Laughing Mad: Izuku gets this after Butterfly exposes himself to his classmates and teachers, a testistament that he wasn't going insane.
- Like a Son to Me: How All Might feels about Izuku. Even if he’s a murderous monster from another dimension.
- Like Parent, Unlike Child: While Racing Stripes and Cheat-A are gung-ho about being professional heroes, their son Horten dreams of becoming a professional artist. Thankfully his parents are cool and accepting of his dream.
- Major Injury Underreaction: Izuku’s response to falling for several metres to be saved by a crash mat made by Yaoyorozu, almost snapping his neck on impact and instead fracturing or breaking his bones, and falling unconscious for six seconds or so during a training exercise? Take out the rest of the giant robots, of course.
- Marionette Motion: Butterfly sometimes moves like this.
- The Maze: The final trap against Butterfly is to lure him into a man-made maze deep within the school. The trick is that Butterfly can dimension hop only if a location exists in the same area in the two dimensions. So leading Butterfly underground would ensure that he can't escape to his home dimension.
- Mobile Menace: Butterfly is proven to be quite unattainable because of a teleportation Quirk. It's eventually revealed that Butterfly actually dimension hops between his reality and the current one in order to make his escapes.
- Not Quite the Right Thing: One night, Bakugou discovers a black feather in his room and destroys it. His reasoning being that bringing it up would trigger Izuku so he was doing him a "kindness" by not bringing it up. It comes back to bite him when the villain is real all along and the teachers insist that the students tell them if they notice anything suspicious no matter how small it may be.
- Not the Fall That Kills You…: Deconstructed. During a hero themed test, Izuku ends up having a seizure while four stories up in the air. He survives thanks to Momo creating a crash pad just seconds before hitting the ground but he ends up dislocating his shoulder and breaking his arm. The brutal injuries, mixed with Izuku trying to fight the robots afterwards, results in Aizawa banning him from future hero exercises until he recovers.
- Nothing but Skin and Bones: The state of Butterfly’s body underneath his clothes is this; turned up to eleven since it’s revealed from All Might’s perspective.
- Nothing Is Scarier: We never find out what happened to Chuck and Dental Demolition. All that the reader gets is an implication late into the story that Butterfly has Dental Demolition's Quirk, at the very least.
- Original Character: From the country town of Jakku, we have Racing Stripes and Cheat-A, a Pro-Hero battle couple, their son Hanten who wants to be an artist, and their sidekick Pathfinder, a serious man who can track other people.
- Pajama-Clad Hero: Aizawa, Present Mic and the other teachers were wearing their sleepwear while trying to hunt down Butterfly who attacked Izuku in his dorm room.
- Parental Neglect: Hisashi Midoriya definitely shows shades of this. He hasn't spoken to his son in months and doesn't make an effort to do so, especially when Izuku begins to experience trauma since the start of Jakku. He also shows more attention to his son after he gains a Quirk and becomes a successful hero hopeful. It's no wonder Izuku is quick to refer to Toshinori as his dad.
- Power Parasite: What makes Butterfly so scary is that he can steal the Quirks of heroes, civilians and even villains which adds to his Super Power Lottery. It's later revealed that he can do so because he was given All For One.
- Properly Paranoid: Izuku. Oh, Izuku.
- Recurring Dreams: The whole of 1-A, except for Kirishima, has ones that end in their own deaths. Most of the class dream about dying in the USJ attack or the aftermath, except for Bakugou, who dreams about the Sludge Villain incident. This is because they are not dreams, but rather, their deaths in Butterfly’s home dimension. Since Kirishima was inspired to apply to UA because of the way Midoriya saved Bakugou in the main timeline, he doesn’t die.
- Reset Button: One of Butterfly's Quirks allows him to reconstruct any room or area he was in as if it was never occupied or ruined. This contributes to him gaslighting Izuku by making it so there's nothing wrong in the area Butterfly appears in.
- Security Blanket: Izuku ends up digging up his old All Might plushie for comfort as his anxiety worsens.
- Shadow Archetype: Butterfly is seen as what would have happened to Izuku if he completely gave up hope in becoming a hero and didn't have a network of supportive friends and adults like the original.
- Shout-Out:
- Izuku and All Might frequently discuss A Sound of Thunder along with the Butterfly Effect.
- An ongoing subplot involves the 1-A kids making projects based on the DC Heroes.
- Spotting the Thread: Butterfly pretends to be Izuku in order to infiltrate one of their shelters and steal a security card. Only Bakugou and Eri notice that something is wrong based on his bizarre demeanor and how he didn't give the little girl a hug like he always does.
- Supernatural Fear Inducer: One of Butterfly’s capabilities.
- Super-Persistent Predator: Butterfly.
- Talking the Monster to Death: After Butterfly appears before Toshinori who realizes that he's another version of Izuku, the aged hero tries talking to him as peacefully as possible to avoid upsetting him. He even tries to clean some of the dirt in his wings and hair.
- That's What I Would Do: Realizing that Butterfly is Izuku, the Pro Heroes turn to the original Izuku for ideas on what he would do given his current situation. And to his displeasure, Izuku correctly deduces that his Evil Counterpart would try to gain more powerful Quirks before hunting him down and pulling a Grand Theft Me.
- Throw the Dog a Bone: At some point, Nezu and Aizawa decide to send Izuku on a long road trip while escorted by various Pro Heroes in order to evade Butterfly. To his displeasure, he's constantly on the move and he doesn't even know where he's going. In the end, he finds out that he'll be staying with All Might in his personal apartment suite.
- Took a Level in Kindness: Pathfinder, a disgruntled jerkwad who did not enjoy having to work with the Yuuei kids, becomes alot more thoughtful after the trauma Izuku and his friends had to deal with. He also becomes more mellow after Butterfly steals his Quirk.
- Tragic Keepsake: One of the items that Butterfly carries from his home dimension is Inko's family album.
- Tragic Villain: Butterfly is regarded as such by the Pro Heroes, Inko and Izuku himself. There's no denying that he was a twisted monster who murdered countless lives without a care and terrorized Izuku, his friends and the Pro Heroes for months on end. But many of them can't help but feel sorry for him as he was once a young dreamer who was corrupted by forces beyond his control.
- The Unfettered: Butterfly will stop at nothing to replace this dimension’s Izuku.
- Unwanted Assistance: Played for Drama. As Izuku's mental health begins to worsen mixed with his mysterious seizures, his classmates and teachers begin to look after him more and tend to his needs. This makes Izuku feel emotionally worse as he doesn't want to be treated like a baby and it makes him feel frustrated that he can't take care of himself anymore.
- The Villain Knows Where You Live: The villain followed you back to your school dorms. The villain followed you to your home, where your mother will be returning soon.
- Villain Takes an Interest: Himiko Toga decides to go after Butterfly after she learned from a civilian that the villain was after Izuku and we all know that no one is allowed to hurt him but her.
- Wham Episode: Chapter 14, where Butterfly is seen by someone who isn’t Izuku for the first time, and the teachers finally believe him.
- Chapter 24, in which Butterfly’s true identity is revealed.
- Wham Line: So many game changing one liners, so little comfort...Tsukauchi: “They found feathers clean enough for a DNA test… It’s related to you.”All Might, to Butterfly: “I-Izuku?”
- What the Hell, Hero?:
- All Might, Aizawa and Inko are displeased with Izuku for neglecting to tell her about his ongoing panic attacks and injuries.
- Both Aizawa and All Might chew out Bakugou for destroying Butterfly's feather and not revealing that he knew about it early on. It's worse since he confesses to this after the villain reveals itself to everyone.
- In the last chapter, Aizawa quickly chastises all of his students for expressing eagerness in celebrating Butterfly's death. Part of his reasoning is because celebrating the death of another is just insensitive for any hero mixed with the untold truth of Butterfly being an alternate version of Izuku.
- With Great Power Comes Great Insanity: Butterfly!Izuku was turned into a vessel for All For One to store his many Quirks. And just like the Nomus before him, his mental state began to deteriorate because of the incompatible Quirks bestowed upon him along with the ones he took of his own free will.
