Logical Weakness / My Hero Academia

My Hero Academia

All spoilers are off. You Have Been Warned!

Logical Weaknesses are pretty much ubiquitous in this series which repeatedly drives home the point that Quirks are physical abilities subject to bodily limits.

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In General

• Quirks relying on close-range combat and/or touch are limited by a user's ability to get close in the first place. Against clever opponents or those with mobility and range-based Quirks this becomes a problem.
• Quirks needing concentration and focus can leave their users strained to the point of exhaustion.
• Quirks can also be subjected to a user’s emotions, state of mind and physical well-being; in addition they always require training to master.
• Even with hereditary components most Quirks don’t grant Super-Toughness and while users can be born with or somehow gain the Required Secondary Powers they still have limits.
• Users can be resistant to the effects of their own Quirks but not immune.

• Izuku Midoriya/Deku can use One For All to amplify his physical strength, speed and durability as a form of Magic Enhancement but it still puts enormous strain on his body. At first he literally can’t use it without severely injuring himself and even after practice and training he can only use a tiny portion of its total power safely. Most of Midoriya's troubles with One for All seem to stem from the fact he was given the power rather than being born with it so he lacks both the physical conditioning and years of experience most people gain from having Quirks at a young age.
• Katsuki Bakugo/Great Explosion Murder God Dynamight doesn't suffer full recoil when Having a Blast but does suffer some, can injure himself if he overuses his powers and has noted his arms going numb in the past. His explosions are also created through his sweat glands so they’re less effective in lower temperatures and generally require time to warm up.
• Gravity Master Ochaco Uraraka/Uravity experiences symptoms of vertigo if she overuses her power, especially on herself. After overusing her Quirk she can get so nauseous that she'll throw up.
• Tenya Iida/Ingenium II and his brother Tensei Iida/Ingenium I have Super-Speed courtesy of a set of engines in their legs which need to shift gears and can overheat or become clogged if not properly maintained. They also can’t use the engines if they experience a loss of function in their lower bodies, something a certain Hero Killer takes advantage of to cripple the first Ingenium, thus ending his career.
• Momo Yaoyorozu/Creati can create objects from her body but needs materials to create them and must understand the specifics of exactly what she’s creating (i.e. to create salt she must be aware "salt" consists of NaCl). She's a Big Eater to compensate but is still limited in how much she can make at a time. Since the objects come out of her skin (it's really not as bad as it sounds) she's limited in how large of an object she can make and often has to make bigger things in pieces. She also has to be a Teen Genius just to understand the necessary science to even use her Quirk in the first place.
• Shota Aizawa/Eraser Head can nullify the Quirks of others by staring at them but must maintain his line of sight and cannot blink while doing so. This has resulted in eye strain and dryness from prolonged use. He also can't nullify mutation-type Quirks since they're part of the user's body and are always on. After losing an eye during a pivotal battle the utility of his Quirk becomes severely diminished, almost to the point of uselessness.
• Shoto Todoroki overheats when using his fire powers and freezes over when using his ice powers while the former and latter are also the Logical Weakness to his father Enji Todoroki/Endeavor and mother Rei Himura-Todoroki. He was the product of an Arranged Marriage for the specific purpose of creating a child with a hybrid ice-and-fire Quirk whose weaknesses would cancel each other out. However, he still has weaknesses: Since he emits fire from his left side and ice from his right at close range he has difficulty getting the correct one pointed at the enemy. He also has difficulty using them at the same time since they just cancel themselves if he's not careful and switching can give enemies an opening.
  • His brother Toya Todoroki wasn't so lucky as he got an extreme version of his father's powers… but inherited the weakness to fire from his mother. He’s better known as Dabi of the League of Villains. You know, the guy who basically has his burnt skin stapled to his body?
• Fumikage Tokoyami/Tsukuyomi has a Living Shadow that becomes weaker in bright places; vice-versa being in darker places strengthens it. This results in Tokoyami losing control since being a separate entity means it’s under no obligation to obey him once it gains enough power.
• Denki Kaminari/Chargebolt short-circuits his brain and temporarily becomes a dullard incapable of fighting back if he unleashes his full Shock and Awe. He also can't control electricity after he discharges it, meaning he either needs to manually make a circuit for it (which he later gets gadgets to help with) or fire his Quirk off every which way and really hope he doesn't hit any allies.
• Kyoka Jiro/Earphone Jack's headphones mean she's vulnerable to loud sounds.
• Yuga Aoyama/Can’t Stop Twinkling’s Navel Laser is useful when it comes to illumination and destructive power as well as long-range transportation but as the power literally comes from his navel he risks the chance of damaging his insides as well as triggering stomach ailments. He’s also vulnerable to attacks coming from the sides and back due to the laser's unidirectional propagation. This is because Aoyama was never the original user as similar to Midoriya he was given the Quirk, but by All For One in order to infiltrate U.A.
• Minoru Mineta/Grape Juice, who can pull sticky balls from his scalp begins bleeding if he pulls out too many in a short time frame. They are attached to his head after all.
• Tetsutetsu Tetsutetsu/Real Steel can turn his body into solid metal but grows weaker if repeatedly hit with something hard and needs to keep up a heavy diet of iron to strengthen his Quirk.
• Neito Monoma/Phantom Thief can copy the Quirks of those he touches but can only use one Quirk at its base state. One for All is a "dud" to him because he can only copy its power stockpile aspect and doesn't have the time to build up a stockpile. This applies to any Quirk that requires accumulating power — since he has no time for the accumulation to occur he can't use it. He's also limited by his own knowledge and abilities. Quirks with physical requirements may be unsafe or unusable for him and of course he’ll lack experience with Quirks he copies unless he's used them before.
  • Monoma later inverts this into a Logical Advantage: if he copies a Quirk that was weakened or crippled in some way he instead gets a base-state version of that Quirk lacking the original's weakness. He ends up copying Aizawa's Erasure. At the time Aizawa had lost an eye, therefore losing the ability to use his Quirk; Monoma has no such weakness.
• Mirio Togata/Lemillion possibly has it worst: He can make himself intangible but has none of the Required Secondary Powers. While intangible he can’t see, hear or even breathe as every particle travels through him. He’s also still affected by gravity so every act of passing through things becomes a complicated process so he doesn't fall through the ground, though thankfully he is immune to Tele-Frag. By the present he's practiced enough to put the 'awesome' back in Difficult, but Awesome but for a while the Quirk was worse than useless. He also phases out of most clothing while using his power, leaving him naked: His hero suit was created using fibers from his hair so he wouldn't accidentally phase out of them while on the job.
• Kai Chisaki/Overhaul can disassemble or reassemble anything he touches, thus making him extremely dangerous for close-range battles as well as limited long-range since he can reassemble objects long enough to hit opponents with. He can also heal himself and others with his touch, making him an excellent Support Party Member as well. But in a similar vein to the “close-range” weakness listed if his opponent zig-zags too much he can't use his Quirk on them. Mirio's Quirk is also this to him and if his arms are taken out in a way he can't react before touching anyone else, like in a surprise attack or while he’s restrained which Shigaraki and Mr. Compress take full advantage of in revenge for Magne's murder he’s completely useless.
• Hitoshi Shinso can Mind Control anyone who speaks to him, but only if they verbally respond to what he says. Anyone who knows this can safely avoid its effects by remaining silent. His Quirk also won't activate if his voice is electronically altered such as speaking though a megaphone or electronic voice-changer since technically the voice would be the device's and not his. He compensates for this with a special mask that can alter the sound of his voice without a filter though it requires precise adjustments.
• Kuroiro can possess any shadow or anything black but can't just teleport between or out of objects, needing to physically move to the thing he wants to merge with next and to be able to reach a point where a shadow ends and light begins in order to teleport out of one. During the Joint Training Arc, Tokoyami traps Kuroiro in his own cloak and keeps it separate from anything else so he can't escape.
• Komori can produce spores that cause mushrooms to grow instantly wherever they land. However, they're still mushrooms which means they need at least some moisture in the air in order to grow and can be killed by certain substances. Hagakure and Tokoyami exploit this in their match in the Joint Training Arc by coating their bodies in ethanol spray.
• This is exploited in the Final Exam arc which pits a pair of students against the teacher they'd have the most trouble with (the teachers are going easy on them; the purpose of the test was to see them face their weaknesses, not get curb-stomped).
  • Kirishima and Sato, who have time limits on their powers fight against Stone Wall Cementoss who can easily beat them in a battle of attrition.
  • Yaoyorozu and Todoroki, the students most dependent on their powerful Quirks are up against mobile Power Nullifier Aizawa.
  • Kaminari and Ashido aren’t the brightest so they face Principal Nezu.
  • Ojiro and Iida face Power Loader who destabilizes the ground so they can't get any leverage to use their abilities.
  • Sero and Mineta, whose Quirks are mostly used for sticking others in place are pitted against Midnight, whose Quirk can put them to sleep without her needing to move an inch.
  • Squishy-but-mobile Tokoyami and Tsuyu are pitted against Ectoplasm, who can use his power to corner them.
  • Jiro and Koda's Quirks both rely on sound so they go against Present Mic and so forth.
  • Deku's One for All is still in a development phase while Bakugo is a close-combat master in a heated environment. All Might can overpower them simply by being fast enough for both.
• Hawks has feathers that he can control telekinetically. It's a very versatile Quirk that he uses to great effect, essentially giving him flight, telekinesis and a dangerous weapon all in one — but he's still limited by the fact that he only has so many feathers which means he can only do so many things with them at once. The feathers are also vulnerable to being destroyed in battle, after which he'll need time to regrow them.
• The Nomu brought to the training dome has a shock absorption Quirk which lets it survive even a full Detroit Smash from Midoriya. But as All Might notes it's shock absorption and not shock nullification which means there's a limit to how many impacts the Nomu can take, a limit All Might's relentless blows eventually surpass.
• Re-Destro can use the everyday stress he accumulates to increase his strength and size but that only extends to his body which means the prosthetic legs he gets after a fight with the League remain the exact same no matter how strong he gets and even snap under his weight.
• Lady Nagant subverts this. During their fight Midoriya attempts to capture Nagant by using an entire office building as cover to close the distance, reasoning a sniper like her would be vulnerable in close quarters. Unfortunately for him she's been trained to deal with close-range fighters, worming her way out of his grip before assailing him with a barrage of bullets from all directions. It's played straight later on, however; for all the power and combat abilities her Quirk has it ultimately boils down to having a sniper rifle in her right arm. Exclusively her right arm. Shattering it effectively renders Nagant powerless and unable to use her Quirk despite still being capable of moving on her own.
• Mount Lady's Quirk lets her grow into a giantess at 67'8" (2062 cm) tall. And while her costume’s been designed to grow with her this doesn't include shoes so she has to be careful not to hurt her feet. Also, being big means it's easy to cause property damage so she tries to grow in spaces that can contain her — when she grew into a giantess in the middle of a crowded city she was shown having to be extremely careful with her movements lest she hurt innocents. Also, Giant Equals Invincible is not a thing with her; she's certainly stronger and tougher than the average person when giant but can still be hurt by other Quirk-users if they're powerful enough. Plus, just like with her feet not being able to have shoes her costume can't contain padding or armor to help her cover this weakness since it can't grow with her. All For One even put her on the receiving end of a One-Hit KO when she was in giant form, both to show his own power and that she wasn't invulnerable.
• Toru Hagakure has invisibility as her power which leads to her having to spend most of her time naked in order to be effective since she can't make clothing invisible. She also can't turn it off, even if she's sleeping or unconscious so she has to be careful of things like cars or obstacles in the environment that won't see her. Finally, it's mentioned that extreme heat or extreme cold makes her very uncomfortable. And since she has to be naked to make the most effective use of her Quirk this can lead to things like coughing or sneezing giving her away. Also, Todoroki once stopped her completely by using his ice powers to freeze her to the ground, mentioning that if she moves the ice would cause her to tear the skin off her feet. Toru is good for espionage and little else because of her Quirk; even then it comes with several caveats and ways that she could still be detected. Even after her Quirk is expanded to be a light refraction ability instead of just invisibility she's still not much more useful than before. In fact, it's shown that this power can be overtaxed when she uses her refraction to deflect a blast from Aoyama and becomes completely visible.
• Cathleen Bate/Star and Stripe's Quirk allows her to assign "rules" to a target she has touched and called out their name, limited to two at a time. But in order to use this she needs to touch a target and call its name. Thus if she does not know the name or the person is experiencing identity issues such as Shigaraki’s struggle with the merged consciousness of All For One then her power is ineffective. Furthermore, because of how powerful her Quirk is she can only create two rules at once. In most cases she can use the first rule on herself, leaving her able to switch the second rule on the fly. If she has to use more than two rules she needs to cancel one in order to create a new one. In addition, Star's Quirk is hampered by her personality much like Sir Nighteye's was: While almost always using one rule to give herself Super-Strength she has a hard limit to how much stronger she can make herself as All Might left such a lasting impression that she can't imagine surpassing him.
• Koichi from the Vigilantes spin-off can repel objects from his hands and feet and also reverse the force to stick to surfaces. This means he can anchor himself to whatever he's standing on and use the repelling force of his palms as shields that allow him to deflect blows or objects. However, all of this is dependent on his weight and strength so anything too big or heavy for him to stop, he can deflect or alter the course but not stop it.
• Nemuri Kayama/Midnight has the ability to put anybody to sleep with her Quirk which shows up as a violet mist. However, someone holding their breath will prevent this from working. While someone can't hold their breath forever they can at least do so long enough to get away if they know she's coming. Also, it takes time to take effect so it's not an instant knockout. Finally, Midnight can only eminate this gas from her body which means she has to get up close and personal for it to work. This can be exploited with long-range Quirks simply staying out of Midnight's range or Mineta's sticky orbs keeping Midnight locked in place and unable to reach him with her Quirk. This is also what leads to her death as a sneak attack from Mr. Compress leaves her heavily injured with a group of villains running to attack. She simply can't create enough gas to cover them in time and is Killed Offscreen.
• Eri has a unique Quirk: "Rewind", which lets her literally turn back the clock on the body of anyone she touches. While this may sound like an awesome Healing Hands Quirk it has the potential to kill as a body she rewinds can have old wounds reopen and life-saving medical procedures undone. When her power first manifested she accidentally rewound her father to the point that he ceased to exist; the combination of her inexperience with this Quirk and the resultant trauma compounded by the abuse she suffered while held captive by Overhaul only made it harder for her. It isn't until she’s freed from his grasp and taken into a loving, caring environment that she’s able to start learning to control it. This is what allows her to restore Mirio's Quirk after it had been lost to one of Overhaul’s anti-Quirk bullets by rewinding his body back to before he was struck with the bullet.

Movies

• Wolfram can create structures out of metallic substances and materials. Unfortunately they still have limits to their overall durability which is exploited by All Might and Izuku.
• Nine can change weather conditions which he uses to create storms and lightning. However, for some reason it causes cellular degradation which results in occasional bouts of extreme pain that leave him incapacitated.
  • After getting additional Quirks through receiving a copy of All For One he gains the weaknesses of those Quirks as well: A shield of solid air can only take so much damage, lasers and wind blasts can be dodged, detection can be avoided, an extra limb that’s only projected can be dispelled and some forms of cellular regeneration don’t affect certain blood types. Carrying all those Quirks and using them in rapid succession only makes his physical breakdowns more frequent.
• Flect Turn can redirect impacts to their source and even briefly store them for later. Though if he tries taking in the energy from repeated blows he’ll start moving when hit, release less power and eventually be overcome.

All For One

As powerful as Shigaraki/All For One is, like any person and/or Quirk he has weaknesses stemming from both his nature and that of his Quirk. Unfortunately for him the heroes figure them out and exploit them repeatedly, especially during the Final Battle.

• To start off the very nature of his Quirk's function and accumulated powers over the generations means he actually has more logical weaknesses than any single Quirk-holder in the series and regularly gets taken off-guard by opponents finding ways to circumvent his powers. In contrast to Izuku learning how to balance or cancel out the disadvantages of his less multiple powers through careful handling the sheer amount of Quirks All For One has means he realistically can't keep track of the downsides in using them.
• All For One's power is seriously good but doesn't come with instruction manuals for the Quirks he steals. If he wants to be able to use individual Quirks to the levels of their original holders he'll have to train with said Quirks like the real users did and since he has so many Quirks he's average at best with using any individual ones. This is why he prefers Boring, but Practical and Simple, yet Awesome powers like Super-Strength and Super-Toughness over Difficult, but Awesome powers like Best Jeanist's control over fibers since he can't afford to put in the time to train it to awesome level. Most of the time he depends on sneak attacks or fighting dirty.
• All For One has to consciously activate individual Quirks as having that many active all at the same time would be extremely impractical. It's for this reason he very rarely uses mass Quirk combinations like the one he tried against All Might, normally sticking to one or two at a time. He still needs time to think about which Quirks he wants to activate and to what effect, as such blitzing him so quickly he has no time to think can prevent him from doing more than frantically spamming Quirks.
• His Quirk has one in that while it can take any Quirk and seems to have no limit to how many Quirks it can take the user does have physical limits the Quirk does nothing to mitigate - and it won't be long before he reaches the limit of his physical strength.
• He's shown repeatedly that while he is capable of stealing any Quirk he can get his hands on except One For All, for his Quirk to activate he needs to physically touch the 'true body' of the holder so anyone fast and agile enough to avoid being grabbed or able to attack at a range can avoid losing their Quirks. He likewise cannot steal Quirks by touching anything they produce such as Twice's Quirk from the cloned variants or Endeavour's Quirk from flaming constructs. Tokoyami Lampshades this weakness as the reason he was selected to provide support with fighting him as Dark Shadow is likewise capable of touching him without fear, allowing him to receive physical blows from somebody other than a holder of One For All.
• Even with a Super Regeneration Quirk he requires constant life support and is dependent on assistance from others for survival.
• His Super Regeneration is strong but has limits like any other. If an opponent can do enough damage in a short enough period it starts failing. Certain types of damage can destroy cells so thoroughly it can't undo the damage without a rest period. It also will automatically work on healing any sort of damage inflicted without distinction to prioritizing which kind of injury is more important than others. Thus if All For One loses an arm and is attacked before it’s fully restored, even if it’s as minor as a stream of electricity only strong enough to stun him; Super Regeneration will slow or even stop healing the limb in order to focus on healing the less serious damage and leave him handicapped for a longer period of time.
• All For One's Quirk means he can't destroy Quirks once he's taken them, just keep them and then pass them on. This bites him in the ass hard when he takes Star and Stripe's New Order after killing her; before dying she placed a rule that made it rebel and attack the other Quirks inside him when. He has no way to get rid of it without someone to pass it on to so it just proceeds to whoop his ass from the inside out.
• Shinso's quirk allows someone under his control to communicate with All For One without any intent at all, following their master's commands. The Living Lie-Detector Quirk he has works by sensing malicious intent but fails on Aoyama and his parents when they are luring him into their trap.
• Warp Gate is an artificial Quirk made by merging multiple Quirks together, meaning it’s more powerful than a natural Quirk by its nature, including All For One's own warping Quirk. Once the heroes have scattered his forces far enough from one another using Warp Gate, there's nothing All For One can do about it.
• All For One takes a few seconds to steal any Quirk. This means it can be interrupted or allow a counterattack. Star could have ordered New Order not to be stolen if she'd chosen to, she just had something else in mind.
• All For One's Impact Recoil is useless against attacks that don't utilize physical force, such as Endeavor's flames.
• All For One subjugates the vestiges of those whose quirks he's through force of will, in contrast to how One For All's vestiges advise, guide and mentor Izuku in cooperation with his own willpower. Even somebody as overwhelmingly powerful as All For One can be given pause if they attack him in a group effort.
• He lost all sensory organs above his upper jaw during his battle with All Might and has to rely on stolen sensory Quirks to compensate, which doesn’t go so well when his access to his quirks is temporarily disrupted by all of them rebelling against him in unison. After Rewind undoes his disfigurement, he stops using said Quirks, but in exchange, his natural senses can now be disrupted by Quirks that target them, enabling him to fall for an Illusionary target that Camie created.
• All For One is incapable of meaningfully growing as a person due to being The Sociopath and a Narcissist (and is implied to have been born that way). This creates a blindspot in his planning, as the idea people might not react as he assumed because they've changed for the better as people is one he's fundamentally incapable of understanding. This is also implied to hinder his ability to use the Quirks he steals, as his lack of strong emotions naturally means he’s unable to pour his feelings into his Quirks to further empower them and thus only uses them at their base strength. It isn’t until he’s so infuriated at the Heroes in the final battle, that he’s able to charge a laser beam Quirk by fueling it with his rage, and is able to knock out Gigantomachia and Dark Shadow.
  • And when All For One manages to use his rage to empower his Quirks, he goes way overboard with it due to not being used to having strong emotions. As a result, he ends up pushing his Quirks far beyond what his body can handle, which makes them immensely more powerful at the cost of massively damaging his own body. In turn, Rewind automatically heals his injuries at the cost of rewinding his age much faster.
• The rewind energy renders him physically immortal because it rewinds any injuries inflicted on him like they never happened. However, since this is 'rewinding', not actual healing, it means that any heteromorph-type Quirks, like Hawks' Fierce Wings, are reduced to an infantile state on his body, and thus effectively useless in a fight, limiting his available options in this condition.
• His Power Parasite nature makes it a Story-Breaker Power when facing opponents with Quirks, as he can just steal their Quirk and it's virtually over given how most Heroes are dependent on their Quirks. Logically, a Badass Normal won't have any Quirk to steal and are used to fighting more powerful enemies, meaning he will have to actually fight them. Normally not an issue given the sheer power disparity, but if Charles Atlas Superpower is in play, or the opponent is wearing technological enhancements...
• All his healing abilities still need time to heal wounds. As such, damage over time attacks such as a constant electric shock or acid effectively counter it, or in the case of Rewind, continually drain his remaining time at a rapid rate.