MHA: Glory Days

Trigger (トリガー Torigā ?) is a type of drug that increases the power of a person's Quirk, but at the same time weakens their sense of reasoning. Originally, Trigger was created to greatly enhance the power and potency of weak Quirks. However, it began to be used for criminal activities, leading to its prohibition in many countries, including Japan, and making it an illegal product trafficked by mobsters and drug dealers worldwide. Because it is produced in different regions of the world, its quality can vary from place to place. Those produced in Asia are usually of poor quality and their effects only last a few minutes, while those produced in the Americas can last one or two hours. Trigger addicts suffer a side effect after use, which is the change in the user's tongue color to black. This drug is usually injected into the body, but a variant has been developed that only needs to be ingested orally to work. Although less effective than the other form, it lacks the psychotropic element.

Personality: Nighteye was a great admirer of All Might, having watched videos of his exploits and possessing several of his collectibles. He could easily recall events and details of All Might's past heroism. All Might also tried to shape Nighteye's vision of what a hero should be: someone who instills fear in the hearts of villains through power and hope in the hearts of civilians through humor. Apparently, Nighteye was afraid to use his Quirk to a great extent, particularly when it came to foreseeing an individual's future death, as he previously believed that once he saw into the future, that future was set in motion and could not be changed. Quirk: Prediction (予知 Yochi): This Quirk allows him to see another person's future from a third person's perspective. To activate his power, Mirai must first touch the desired target and then make eye contact with them. This Quirk remains active for one hour and, once activated, requires 24 hours before it can be reactivated. The future he sees is shown in great detail (second by second) and has always been 100% accurate. However, recent events seem to suggest that those with a Quirk that alters time in some way can affect the accuracy of their Quirk, possibly making the predicted results questionable and/or null.

Name: Sir Nighteye

Kanji: 佐々木ささき未来みらい Rōmaji: Sasaki Mirai Alias: Sir Nighteye (サー・ナイトアイ Sā Naitoai ?) Birthday: January 2 Age: 20 years old Gender: Male Height: 200 cm Blood type: AB Quirk: Prediction Occupation: Sidekick Family members: None known Acquaintances: All Might (Coworker, Pro Hero affiliate, friend), David Shield (Coworker) Nationality: Japanese Place of birth: Tokyo Appearance: Sir Nighteye is a tall, slender yet fit man with sharp, rather elongated features. His glossy hair is always straightened and parted to the left, a dark green with three yellow streaks framing his face—two on the right and one on the left. His eyebrows are also yellow, matching the rims of the triangular spectacles he wears and the bright yellow irises of his stern-looking eyes. His appearance exuded authority, as he rarely smiled and always seemed dazzling. As an extra fact, it has crow's feet that measure 0.6 cm large. Unusually for a hero, Nighteye seemed to prefer office attire (a white suit with gold buttons, a white dress shirt, and a red tie with white polka dots) to an elaborate superhero costume. However, his clothing appears to be quite durable. Personality: Sir Nighteye maintained a stoic and intimidating presence, with a cold and sharp gaze, but that was only the side he showed in public. Even with his supposedly cruel and intimidating demeanor, Nighteye greatly valued humor and, in fact, required people to make him laugh before acknowledging them. Nighteye believed that humor and energy were vital elements for the future of society and punished subordinates who failed to display these qualities. Although he appeared rather cold at times, he was very quick to jump to the defense of his colleagues and anyone working under him. He was quick and very open about when he made mistakes and defended others who had made errors under his supervision.

When One For All is transferred, the new user's body is not naturally suited to it as they usually would be with a Quirk they were born with (ex: someone who breathes fire doesn't burn their mouth while using their ability). In addition, One For All is a lot to handle; if one's body can't take the power, then one's body could be blown apart. Because of this, the successor must undergo intense and rigorous physical training. Like with all Quirks, the ability to use One For All is strongly tied to the user's physical health and well-being. As such, they will find it harder to handle the Quirk's raw power should they face negative health issues, even if they were strong and physically conditioned enough to inherit it. 

One For All was one of the most powerful Quirks in existence; however, mastering it completely was extremely difficult. It was a transferable Quirk that could be passed from one user to another. Its name stemmed from its nature: being a Quirk for everyone. For the Quirk to be transferred, the recipient had to ingest a sample of the predecessor's DNA (for example, a lock of hair or a drop of blood). Since One For All could not be taken by force, it was one of the few Quirks that could be used in combat against All For One, as any All For One user could steal most other Quirks. One For All's primary ability was to accumulate a massive amount of raw power, enhancing the user's physical capabilities to superhuman levels, resulting in incredible strength, speed, agility, and stamina. For example, even with his power limited by a chronic injury, All Might's punches at 100% could generate enough wind pressure to alter the weather. The user could focus the stockpiled power into a single body part or spread it evenly throughout their body, although focusing the energy puts a tremendous strain on the part of the body where the power is concentrated. The user could also control the percentage of the power they activate. The core of One For All had grown in strength from being passed from user to user, and the Quirk Factors of all of the previous users had merged into the core. The final user, Izuku, could access the Quirks of the previous One For All users. The Quirks had significantly strengthened since their original users used them due to the nature of One For All's core stockpiling power and rising force from user to user.

Long ago, two brothers were born. The older one possessed a Meta Ability that allowed him to steal other people's Meta Abilities and transfer them, while the younger one seemingly had none. [3] The older brother, who now called himself All For One, rose to power, while his younger brother, whom he named Yoichi, was weak and frail, with a very delicate body, and resisted his brother's dominance. Enraged by Yoichi's defiance and in a twisted display of affection, All For One bestowed upon his younger brother a Quirk that allowed him to accumulate power within his body. However, unbeknownst to him, Yoichi already possessed a Quirk whose sole power was to transfer it to another person. The Transfer Quirk and the Power Accumulation Quirk merged to form One For All. Yoichi was freed from All For One's clutches by a resistance leader named Toshitsugu Kudo and his second-in-command, Bruce Lee. Eventually, his brother tracked them down in an attempt to retrieve him, and when they tried to escape, All For One killed him. Yoichi's blood splattered Kudo as he and his resistance fled, and shortly afterward, he began experiencing strange effects on his body. Bruce examined him and discovered that, alongside his original Quirk Factor, there existed another, almost insignificant Quirk Factor, which Kudo understood to be the lingering will of Yoichi, who had died within him. All For One came to the same conclusion after discovering that Yoichi's Quirk had vanished from the left hand he still possessed, and realized that Yoichi was still out there. Yoichi took it upon himself to pass the torch, and this was followed by all his successors until it reached the eighth wielder, Toshinori Yagi.

Full name: David Shield Kanji Name: デヴィット・シールド Rōmaji Name: Devitto Shīrudo Birthday: December 1 Gender: Male Place of birth: California, USA Height: 185cm (6'1") Hair Color: Brown Eye Color: Aqua Quirk: Squirmy Fingers Appearance: He's a slender man, being withe-skinned. He has slicked-back, shoulder-length hair with a loose strand hanging over the side of his face, no facial hair, and no notable wrinkles. He wears a crimson hoodie, with its hood left out over the white lab coat he wore on top. He also wore dark pants and black sneakers with white soles and laces. Occupation: Scientist, Sidekick, Creator of Support Gadgets. Area: Support Personality: Like All Might, David is a generally compassionate and altruistic individual, always looking to create new ways to better society as a whole and help those in need. While having a relatively weak Quirk that is unsuitable for being a Pro Hero, he instead chooses to help heroes by designing costumes and inventing support gear. David is in charge of making All Might's hero costumes. He has an almost blind admiration for his friend, placing a lot of hope in him and doing everything he can to support him, which sometimes leads him to be impulsive if it affects both of them and their well-being and careers. He's quite intelligent, and while he's not a social butterfly, he can easily follow a conversation. He demonstrates fierce loyalty to Toshinori and those he cares about, trying his best to help them, which shows his helpfulness. He seems to be the most adapted to the American environment due to having been born there, serving as a kind of guide for Toshinori when interacting with people and the media, since the American world is very different from the Japanese one. Quirk description: Squirmy Fingers (ぐにゃぐにゃ 指 ゆび, Gunya gunya Yubi? ): David's Quirk allows him to bend his fingers more than a person normally can. He uses this power to perform precision work on the inventions and hero costumes he creates.

Real name: Toshinori Yagi  Kanji name: (八や木ぎ俊とし典のり, Yagi Toshinori?). AKA: All Might (オールマイト, Ōru Maito?) Age: 23 years old Gender: Male Birthday: June 10 Blood type: A Nationality: Japanese Place of birth: Tokyo Family: Toshie Yagi (Mother, Deceased), Father (Status unknown, possibly deceased). Acquaintances: Enji Todoroki (Friendly rival), Nana Shimura (Mentor, mother figure, deceased), Gran Torino (Close friend), Cathleen Bate (Acquaintance, location unknown), Sir Nighteye (Friend, co-worker) Extras: •Toshinori has zero experience with women. •Toshinori is a non-drinker. •His favorite things are movies and the cedars from Yakushima. •His personality is described as "unexpectedly playful". The true details of All Might's Quirk were kept secret, to the point where it was one of the world's greatest mysteries (though most people just assumed it was super strength or invulnerability). Whenever asked about it in interviews, he would simply joke and dodge the question.

Accompanied by the OFA, All Might has developed his own fighting moves inspired by the various US states he has been to. •California Smash (カリフォルニア スマッシュ, Kariforunia Sumasshu?): All Might attacks with a frontal somersault to build up momentum and air pressure and is then released in a smash.Carolina Smash (カロライナスマッシュ, Karoraina Sumasshu?): All Might runs towards an enemy while keeping his hands in a cross position, then in a downwards cross chop to the enemy's head. •Double Detroit Smash (ダブルデトロイトスマッシュ, Daburu Detoroito Sumasshu?): All Might and Izuku use One For All at 100% and combine their Detroit Smash attacks to create a smash more powerful than anything they can accomplish alone. First used this move to defeat Wolfram.[17]Missouri Smash (ミズーリースマッシュ, Mizūrī Sumasshu?): All Might runs towards an enemy while keeping his hand flat and hits the enemy on the head while running past them in order to knock them out. •Detroit Smash (デトロイトスマッシュ, Detoroito Sumasshu?): All Might performs that same attack as Texas Smash except this move is with a downward punch instead of a straight punch. The punch is powerful enough to create a shock wave large and powerful enough to clear the weather. •Nebraska Smash (ネブラスカスマッシュ, Neburasuka Sumasshu?): While throwing a punch, All Might rotates his arm to create a tornado. •New Hampshire Smash (ニューハンプシャースマッシュ, Nyūhanpushā Sumasshu?): All Might punches the air while in the air to propel himself backwards towards his enemy and smashes his body into the enemy, crushing and injuring the enemy with his great weight. •Oklahoma Smash (オクラホマスマッシュ, Okurahoma Sumasshu?): All Might whirls around while enemies have latched onto him, spinning with enough force that when they are released, they are easily thrown through concrete. •Texas Smash (テキサススマッシュ, Tekisasu Sumasshu?): All Might throws a punch in order to create wind pressure in order to blow objects and people away.

All Might still keeps a keen intuition and sharp reflexes, which helped him hone his skills as a Hero ever since he acquired his powers. Some of his other abilities are: •Trained Muscles: Usage of One For All requires the user to have strong muscles, as One For All is a lot to handle and could cause the user's body to be blown apart if they don't possess the necessary body strength. Gran Torino said that Toshinori, in particular, had a strong body that allowed him to master One For All much faster than previous users. Willpower: Toshinori possesses a remarkably strong will, especially in critical moments involving the lives and well-being of others. He will do everything in his power to achieve his goals and keep everyone safe. He also applies this determination to his personal life. •Overwhelming Strength •Immense Speed •Overwhelming Durability •Immense Stamina

Many compared Toshinori's personality to their mentor Gran Torino, since both play dumb quite often. Toshinori is far more intelligent and perceptive than his campy image would suggest. He has a tactical mind regarding battle strategies and public speaking. Assessing a Villain's threat level, Toshinori skilfully applies the necessary force and avoids injuries when possible. If he's in control, he even makes dramatic performances out of their defeats as examples to other Villains. Even when outnumbered, pitted against Villains who are much larger in size, and faced with several catastrophes, Toshinori took on every scenario with his head held high, being able to save people and defeat Villains faster than any other Hero.  Toshinori always prioritizes the lives of others over his own, considering them his responsibility. Still, Toshinori is deeply aware that saving everybody in the world is an impossible task, which is why he sought to become a Symbol who could inspire others to take action as well. Another negative aspect of Toshinori's drive to be the Symbol of Peace is that he tends to have a self-deprecating view of himself, not seeing himself as the paragon most people view him as, but instead feeling the full brunt of his responsibilities (though he can at times be humorously self-absorbed). Due to the stresses of acting like the ideal Hero while fearing being found out in his Hero persona, he seems to have developed a minor case of imposter syndrome. Toshinori has a fatherly attitude towards childs and teens. All Might has the habit of adding "young" (少年, Shonen?) to the surname of his students whenever he is speaking out loud or thinking to himself.

His smile, a gesture that served to calm others, started becoming more of a way for Toshinori to hide his fears and insecurities from the general population. Above all else, he considers self-sacrifice the most noble action, coming in many forms for Toshinori, such as physically on the battlefield, and mentally, sacrificing so much of his time that he barely has a private life.  This selflessness has aided Toshinori well to become a symbol, as civilians trust his words, "Do not fear", truly knowing he won't hesitate to save them. The dismissal of his safety eventually caught up to him, causing issues with his work and personal life. Toshinori always prioritizes the lives of others over his own, considering them his responsibility. Still, Toshinori is deeply aware that saving everybody in the world is an impossible task, which is why he sought to become a Symbol who could inspire others to take action as well. He's aware of Villain tactics, such as monologuing, and actively ignores them. Only the most manipulative of Villains, like All For One, can bring out rare instances of anger in All Might, such as catching him off guard and giving him a mortal injury, as well as mocking his late master, Nana, causing Toshinori to rise in anger, saying that he would destroy All For One's wicked ambitions and bitterly stating that the Villain would die in prison.

Since his youth, Toshinori had always carried a single yet burdensome goal: to become a pillar of hope that people could always rely upon during harsh times. After obtaining One For All from Nana, Toshinori would become not just a Hero, but a legend, thanks to his seemingly endless competency and charisma. No matter who or what he faced, Toshinori would stand up triumphantly every time, one battle after another, inspiring the world and sending fear into the hearts of Villains everywhere. Toshinori has a chronic ability to save as many people as possible, a trait shared with his successor. He exhausted himself and fell behind on his other Hero duties, such as filing paperwork. Though he was embarrassed by it, he still gratefully accepted the offer of Sir Nighteye to file his reports.

Toshinori's Hero persona as All Might appears to be derived from comic book superhero stereotypes: exuberant and filled with dramatic flair. He always protects and saves innocent people with a huge smile. The habit of smiling was ingrained in him by his mentor, Nana Shimura, who believed that the ones who smile are the ones who are the strongest. Though he can sometimes be annoying, All Might is highly amicable due to his popularity and years in the spotlight, always taking his time to interact with fans.

Once Toshinori reverts to his true form, he becomes reserved and solemn, avoiding attention in direct contrast to the grandiosity of his Hero identity. While he's an optimist, he still ensures his goals are grounded in reality.

Toshinori usually switches constantly at work between his Civilian Form and his Empowered Form, using the latter in combat and to present himself to the cameras most of the time.

In his empowered form, Toshinori is a towering figure with a powerfully muscular and well-defined physique, resembling a classic Western comic book superhero. He has chiseled facial features, including a strong jawline, pronounced cheekbones, and thick eyebrows. His short blond hair is swept backward, with two distinct tufts that stick up slightly to each side on the front, forming a 'V'. However, it still contains some soft and youthful features. In his Civilian Form Toshinori is a lean but fit young man, his hair is wavy, with two long strands coming down from his hairline and framing his face. In general, his facial features were noticeably softer, along with not having shadowed eyes on his face as his future self. His eyes are a deep blue, and a white skin.

In his Empowered Form he measures around 2.20 meters, which is quite tall. In its Civilian Form, it is a little shorter, but that doesn't make it any less remarkable among the crowd, standing at 1,97 meters tall.

During his job, he wears his official Hero Costume, which consist of a dark blue, form-fitting suit with red and white accents on the sides, a yellow belt with a gray buckle, armored white gauntlets and boots with yellow trim and soles. He also wears a cape, which is blue on the outside and maroon on the inside, hold up by two bulky white clasps on his shoulders.

In his Civilian Form he usually wears somewhat loose-fitting clothes, so that when he has to transform into his Empowered Form these clothes fit snugly.

Gran Torino, after the beating, reminded Uagi of his new responsibilities as successor to his recently deceased mentor and how he should carry the torch, reminding him of Nana's sacrifice to motivate him to continue. After graduation, Toshinori continued his journey as a now-certified Pro Hero, deciding to change course by traveling to America, the land of opportunity, in search of more experience and recognition. He arrived in a territory that remained hostile to foreigners attempting to become Pro Heroes. Shortly after settling in, Toshinori met David Shield, nicknamed Dave by himself, who was an inventor/scientist. Although his Quirk seemed useless at first, David Shield was quite skilled at using it to build things with ease. They became friends, with David becoming Toshinori's sidekick and later his best friend, fighting together against the dangers of the various cities they visited. They were constantly on the move, traveling from state to state to provide aid and support. One For All helped Toshinori quickly climb the ranks of American pro heroes, gaining increasing fame and recognition from the media and the public, although some people in the country remained skeptical of him and his intentions. His heroic acts and charisma on camera made him quite beloved by many. In the end, he ended up allying himself with Sir Nighteye, another sidekick of his who, like him, was located in America, serving as a sort of secretary for Yagi. He met Cathleen in a Texas town, having saved the girl from an altercation caused by some villains. They became good friends and even took a picture together. All Might became a source of inspiration for that girl.

Toshinori showed great potential in his studies, earning good grades in multiple subjects and performing optimally while continuing his training with his mentor, attending her practice sessions in the afternoons. During this time, Toshinori developed a close bond with Nana Shimura, seeing her almost as a mother figure. In his third year at U.A., his mother, Toshie, died in a villain attack, unable to save her in time before she succumbed to her injuries, leaving him an orphan. Nana found help in Gran Torino, a friend who shared her ability to fly, albeit in a different way. While Nana Shimura was more patient with Yagi, Gran Torino was more grumpy and strict with the boy, pushing him to train late into the night and to his limits, being harsh in both words and actions. However, Gran Torino valued him as much as Nana did, pushing him to improve if he wanted to become the Symbol of Peace he had dreamed of since childhood. In class at UA, Toshinori faced a new rival, Enji Todoroki, better known as Endeavour, his current hero name, a boy with a fire Quirk from the same class as Toshinori. While Yagi saw this rivalry as friendly, Enji viewed it more as a competition to overcome, vying with Toshinori for the title of Symbol of Peace for several years. Toshinori gradually developed more control over OFA becoming quite outstanding in his class, Class 1-A. However, everything came to an end when Nana Shimura had to face All For One in an abandoned hangar. It was a fight that ultimately had no solution and no happy ending, and she was accompanied by Toshinori and Gran Torino. In a final act, Nana passed the torch to Toshinori, her last words being, "Next, it's your turn," before being annihilated by All For One. Before she was killed, she begged Gran Torino to take Toshinori away before the hangar exploded. In a safe and distant location, Toshinori collapsed to the ground, overwhelmed by helplessness and shock. Gran Torino then beat him to bring him out of his crisis.

Toshinori Yagi (八や木ぎ俊とし典のり, Yagi Toshinori?), also known as All Might (オールマイト, Ōru Maito?), also bears the title of the world's Symbol of Peace (平和の象徴, Heiwa no Shōchō?).

All Might was the eighth holder of the One For All Quirk after receiving it from Nana Shimura.

Toshinori was born somewhere in Tokyo, Japan, an only child. His mother, Toshie Yagi, had always been a pillar of strength in his life, supporting his dream of one day becoming a Pro Hero. Meanwhile, his father wasn't very present, traveling frequently and consequently not having many memories of him. He used to read a lot with his mother, especially the Japanese comics of Anpanman, one of his favorites. From childhood, Toshinori aspired to be a Pro Hero; however, he had a small problem: he was born Quirkless, which made his heroic dream seem much further out of reach. Nevertheless, that didn't stop him from dreaming. Even without a Quirk, he always displayed heroic qualities, trying to help people however he could. This continued into his adolescence, and everything unfolded naturally until he met his future mentor, Nana Shimura, in an old alley. A Pro Hero, she possessed One For All, being the third user of this power, and also had a Quirk: Floating. Toshinori defended himself against some thugs using nothing more than a metal pipe he found lying around. While he didn't accomplish much himself, as Nana did all the work, her admiration for his bravery earned him her trust. Before Nana flew away, Toshinori begged her to teach him how to be a hero like her, thus beginning his training with her. Later, after completing his initial training and when his body was ready to receive such a vast amount of power, he was given One For All. However, the experience of eating Nana's hair was neither pleasant nor hygienic, but it was the easiest way to transfer the DNA with OFA. Finally, at 15, he joined the U.A. Hero Academy in Musutafu, Japan, thus meeting his rival, Endeavor, or Todoroki.

Mutant (異形, Igyō?)-type (also called Heteromorphic) Quirks are abilities that physically modify the user's body, resulting in a permanent "abnormality" directly related to their power. Mutant-type Quirks create bodily structures that grant the user more complex abilities that Emitter and Transformation Quirks cannot safely provide. Often times they will bestow prehensile appendages that the user can control or add structures to pre-existing limbs to enhance pre-existing abilities.  Users with Mutant-type Quirks, most often known as "heteromorphs", also find themselves the most discriminated against, even by other Quirk users, due to their outer appearances

•Accumulation-type Quirks are powers that, in order to function properly, require the user to accumulate something ahead of time, such as power, energy, mass, or a particular resource. Such Quirks of this type include One For All.

•Transformation (変形, Henkei?)-type (also called Composite) Quirks are abilities that cause the user to take on a temporary alteration of some kind. Transformation-type Quirks allow the user to temporarily transform their body in a variety of manners, sometimes enhancing existing features, removing features, or adding new features to the body altogether.

Transformation-type Quirks usually require a conscious effort by the user to activate, though most users can be trained to initiate them reflexively, depending on the conditions required for activation, and practice to initiate their Quirks with greater intent and precision.

Transformation-type Quirks usually require a close-range proximity in order to fully utilize them in combat due to them only affecting the user's body. While Transformation-type Quirks are usually quite powerful, their biggest weakness is that their effects are often temporary, and overexertion usually leads to negative repercussions on the user's behalf. Transformation Quirks can also be limited based on the user, how resilient their body is, and the resources they have available to them.Transformation-type Quirks are the only known type of Quirk that can bestow the user attributes they do not normally exhibit by default. Because this type of Quirk combines the activation time and mutant-shape aspects of the other Quirk types, it is also often known as Hybrid or Composite.

Transformation-type Quirks generally affect the user exclusively.

Transformation seems to be the least common type of Quirk.

Quirks come in a very wide variety, as the name "Quirk" implies they are unique to each individual. However, Quirks can be divided into categories based on what they do and how they function, known as Quirk Types. Some Quirks cause a permanent physical abnormality to the user's body, known as Mutant-type. Some cause the user's body to undergo a temporary physical abnormality when the power is used, known as Transformation-type. Finally, some Quirks don't cause any abnormalities to the user's physical body at all, known as Emitter-type.

Although Quirks are officially classified into just one of three main types, they can exhibit traits of multiple categories.

•Emitter (発動, Hatsudō?)-type (also called Operative) Quirks are abilities that allow the user to generate and possibly control certain things, or alter existing things around them in certain ways. The emissions of Emitter-type Quirks can have a wide variety of properties and abilities. Emitter-type Quirks can also have various ranges. While some users require physical contact to use them, others can have much longer ranges with no distance restrictions.

While most Emitter-type Quirk users generally have a handle on their own "emissions", it's also possible for users to hurt themselves from coming into too much contact with their Quirk. 

Some Emitter-type Quirks cause the user's body to take on a temporary alternation. While such Quirks would normally fall into the Transformation class, the difference is that these powers require the user to take in an outside resource in order for the Quirk to activate.

Emitter-type Quirks are, by a wide margin, the most common type of Quirk.

In an effort to preserve order in the superhuman society, there are several laws and procedures in place to ensure the conscientious use of Quirks. Public display of Quirks is against the law, as is using them with the intention to harm other people, except in cases of self-defense, such as when one is under attack or preventing someone else from being attacked. Since the vast amount of different Quirks can range from harmless to lethal, it is impossible to account for every single Quirk in the law books, leading to the simple strict banning of using one's Quirk to commit bodily harm. Despite this, the notion of Quirks not being used in public is sometimes ignored or overlooked, being compared to an old rule of not riding bicycles on sidewalks, although doing so would still be an infraction of the law. Certain Quirks also have more regulations than others to prevent their abuse. Every citizen who possesses a Quirk must register it within the System, followed by being given a name for it. Children from elementary school onward receive instruction on how their Quirks work and how they function, as well as learning about the regulations governing them and the basic laws that every citizen should understand. Hero schools were established to professionally train the next generation of Pro Heroes, who can operate and use their Quirks in public once they have obtained their Hero License, although they can only do so in emergencies until they graduate.

The theory of the Quirk Singularity (個性特異点, Kosei Tokuiten?, lit. "Individuality Singularity") is a popular line of thinking that suggests that Quirks will continue to mix together and deepen, growing in both strength and complexity with every new generation. Eventually, Quirks will develop to a point where no one will be able to control them anymore.

After the initial manifestation of a Quirk, it is possible for the user to undergo an "Awakening" (覚醒, Kakusei?) later in life. The right emotional catalyst can cause Quirks to evolve (飛躍, Hiyaku?) on the spot, usually requiring the individual to experience intense feelings of stress, like that of a life-or-death situation. This results in one's Quirk gaining a new level of strength and/or new aspects to its nature that were previously not possible.Awakenings are typically considered very rare, to the point that not even All For One could comprehend the concept.

Quirks are inherited genetically through what appears to be Mendelian inheritance. A child will either inherit the father's Quirk, the mother's Quirk, or a completely new Quirk formed by a fusion of the two. Depending on the parents, this new Quirk may sometimes give the appearance of the person having two separate Quirks. Naturally, since Quirks are inherited genetically, siblings tend to have the same or very similar Quirks. In rare cases, a child may manifest a Quirk that is completely different from anything in their genetic lineage, akin to a mutation. Since Quirks are passed on from parent to child, some people had taken to marrying a partner based on their Quirk, what's known as Quirk Marriages (個性婚, Kosei Kon?, lit. "Individuality Marriage"). These were done for partners to conceive a child with a more powerful version of one Quirk or a combination of both. Quirk Marriages became an issue during the second and third generation of Quirk users, as people were forced into relationships under the guise of arranged marriages. The Himura Family in particular became notorious for selling their children off into marriages as a result of their wealth diminishing after years of inbreeding. The concept of creating "custom children" for the sake of experimenting with powers was quickly deemed as unethical by society.

Every Quirk contains an echo of the consciousness of its wielder, known as a Vestige (面おも影かげ, Omokage?). If a person's Quirk is transferred to someone else, the consciousness of the previous wielder will appear in the new user's mind, either as voices in their dreams or as manifestations in a mental mindscape. This phenomenon is compared to cases of people whose personalities and tastes changed after an organ transplant. If further transferred to yet another new user, then that new user will experience the consciousnesses of all of the previous users, though these consciousnesses will disappear if the new user loses the transferred Quirk. While not much is known about these consciousnesses and what they do, they are seen to hold the same personality and memories of their original users up until they are transferred to someone else. It is shown that these Vestiges (who have been transferred to other hosts) can potentially act or override the new host body they reside in. 

Quirk Factors (個性因子, Kosei Inshi?, lit. "Individuality Factor"), also known as Plus Alpha Elements (+プラスαアルファな仕し組くみ, Purasu Arufa na Shikumi?), refers to the collective physical and genetic traits that compose a person's Quirk. This includes the primary Quirk power, as well as the specific body parts that allow said primary power to function properly. Another facet of Quirks is that they are affected by the user's emotions, given that they serve as a part of their physiology. This applies to some Quirks more than others, Quirks are known to have a direct influence on the user's personality too. Some Quirks can even be more of a curse than a superpower to their users, They may be pigeonholed into certain prejudices according to their Quirk, and may be categorized as villains or bad people because of their Quirk.

Quirks usually appear in people at a very young age, most commonly from age four onward, although there are cases where an individual is born with one. When Quirks first appear, there are no warning signs, so they often catch many people by surprise. However, it takes years and training to understand and master them, and children are often clumsy with them. In rarer cases, a single Quirk can take the form of multiple abilities that are completely different from each other, giving the impression of having more than one Quirk. It is even possible, albeit quite rare, for some Quirks to take the form of sentient beings that are connected to their users.

Quirks are extensions of a person's bodily functions. As such, they can be trained and worn out. When a person works out their muscles, the muscle fibers are destroyed and new, stronger ones grow back; this same rule applies to Quirks. However, should a Quirk be overused, the user could suffer any of a variety of drawbacks, depending on the nature of the Quirk. These drawbacks are usually simple ailments, such as dry skin or nausea; however, in some cases, the drawback can be much more severe. The body of a Quirk user has natural adaptations to protect itself from any damage the Quirk might do to them without these natural defenses. For example, someone who can breathe fire does not burn their mouth when using their ability. However, there are instances where a Quirk doesn't suit the user's body and the body can't handle it. Such conditions can be bypassed through the use of support equipment. Some people have bodies that are not properly suited for their Quirk, not even with equipment, these cases are very rare but can be harmful to individuals who have this genetic flaw when using their Quirks.

Currently, roughly 80% of the people who make up the global population possess a Quirk, and that percentage continues to increase. According to Yoichi, the number of individuals without a Quirk has been rapidly declining in population, indicating that now less than 20% of the world's population is Quirkless (無個性, Mu Kosei?, lit. "No Individuality").

The announcement by the researchers proved to be reckless and premature, as it caused division among people and chaos to grow. Meta Ability users were labelled as monsters or diseased, and as a result, Anti-Meta groups rose up with the objective of exterminating those with Meta Abilities. As chaos and unrest ensued due to the outbreak of Meta Abilities, ordinary civilians decided to take matters into their own hands to bring order to society, and thus the first "Heroes" appeared in the form of Vigilantes, beginning the Vigilantes Era. During this time period, All For One became a symbol of unity in society. He used his own Meta Ability to remove Meta Abilities from those who did not want them and give them to those that did. He claimed his actions were meant to help return society to its prior state, when in reality, he was gathering followers who were loyal to him, allowing him to act out his ulterior motives. As society adapted to the new status quo, the Police Force moved to prioritize leadership and to maintain the status quo, and as such, decided not to use Quirks as weapons. To fill that void, the profession of crime-fighting Quirk users, Pro Heroes, began to exist, starting in Rhode Island, USA, which caused the Vigilantes to slowly disappear. Authorizing the use of powers that could so easily kill, however, was a greatly criticized decision at first, but eventually became accepted as a legitimate occupation. This became known as the "Advent of the Extraordinary" (超常黎明期, Chōjō Reimeiki?, lit. "Dawn of the Paranormal").

A Quirk (個こ性せい, Kosei?, lit. "Individuality"), formerly known as a Meta Ability (異い能のう, Inō?, lit. "Extraordinary Ability"), is a superhuman power that a person can possess.

Along with being unique to each user, Quirks are sorted into multiple categories. Quirk users are also limited to only developing one power or set of powers and are thus unable to achieve any other through natural means.

While the cause of this phenomenon is unknown, one research group looking into the matter hypothesized that it was caused by the spread of a previously unknown novel disease carried by mice, while others theorized that it was actually a natural evolution of the human race. However, to date, there is no hard evidence to support any of these theories. The Luminescent Baby took advantage of their fame as the first recorded Quirk user, attempting to rally a following that preached a return to a peaceful and stable society. They had 10 million followers at one point, but was later murdered by Zen Shigaraki, a powerful supervillain who would later be known worldwide as All For One, out of jealousy for all the attention and admiration they were getting. The aforementioned research group announced to the public that those with Meta Abilities were a subbranch of humanity with new genetic factors. The dawn of this extraordinary era was marred by a breakdown of society caused by the sudden onslaught of criminals, dubbed Villains, empowered by their newfound superpowers, as well as ordinary people being prejudiced against the new minority. It suddenly became impossible to define one's self as a normal person, laws and human rights were thrown into constant debates, and the progress of civilization came to a sudden halt.