Quirk

A Quirk (個性) is a special, superhuman ability an individual can possess. Quirks are generally unique to their user, and are classified in multiple categories.

History
The first person to manifest a Quirk was a newborn baby in the city of Quig Quig, China, who had the ability to emanate light from their body. After that incident, many people around the world began to manifest different kinds of special abilities, though the cause of the phenomenon was unknown. Currently, 80% of the world population possesses a Quirk.

At the dawn of this extraordinary era, 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, Heroes, began to exist. Authorizing the use of powers that could so easily kill, however, was a greatly criticized decision at first. Over time, it came to garner public support due to the fact that the first people to work professionally as Heroes acted morally and upheld the law.

Information
Quirks are inherited genetically, and typically manifest in children by the age of four. A child can manifest either one of his parents' Quirks or a composite of the two. As Quirks are said to be the next stage of evolution in the human race, it is possible to diagnose a person as Quirkless by analyzing the presence or absence of an extra joint in their pinky toe: those without the joint have evolved by discarding a body part they don't use, and will likely develop a Quirk; those who still have it have yet to evolve, and, as such, possess no Quirk at all.

It is possible for children to already be born with their Quirks. Such was the case with Present Mic and the very first person to manifest a Quirk, the Luminescent Baby. Although very rare, it is also possible for animals to possess Quirks, such as Nedzu. Under special circumstances, two Quirks may mutate and merge, becoming a new Quirk, as was the case of One For All. It also appears that the physical mutations of mutation-type Quirks can be inherited even if the Quirks themselves aren't, as people such as Fumikage Tokoyami and Kouji Kouda have quirks unrelated to their appearance.

There are several laws and procedures to ensure the conscientious use of Quirks. During elementary school, children receive Quirk counseling, in order to learn how to use their powers responsibly. Public display of Quirks are against the law, except in cases of self defense, such as when one is under attack or preventing someone else from being attacked.

Emitter Class
Emitter (発動) class Quirks have the ability to either release certain substances, or alter materials around them in certain ways. Emitter class Quirks usually require a conscious effort to activate (such as Electrification, Lumber, and Tape), and some even require large amounts of concentration in order for them to remain active (such as Erasure).

Emitter-type Quirks can also have various ranges. While some users require physical contact to use them (such as Zero Gravity) others can have much longer ranges with no distance restrictions (such as Navel Laser). 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 (Explosion). The emissions of emitter Quirks can have a wide variety of properties and abilities.

While some substances produced by emitter Quirks have common properties, some are unique to the user, and thus have special attributes to them. Those who alter the properties of materials around them can also widely vary in effects, from molecular alteration (Softness) to molecular destruction (Disintegration). Emitter-class Quirks are, by a wide margin, the most common type of Quirk.

Transformation Class
Transformation (変形) class Quirks cause the user to take on a temporary alteration of some kind. Transformation quirks allow the user to temporarily "transform" their body in a variety of manners, sometimes enhancing existing features (Hardening, Gigantification) or perhaps adding new features to the body altogether (Dark Shadow, Tool Arms). Transformation Quirks generally affect the user exclusively, the only known exception being Recovery.

Transformation Quirks usually require a close-range proximity in order to fully utilize them in combat due to them only affecting the user's body. Transformation Quirks are also the only known type of Quirk that can bestow the user attributes they don't normally exhibit by default. Transformation Quirks usually require a conscious effort by the user to "activate", though users can be trained to initiate them reflexively. While transformation Quirks are often quite powerful, their biggest weakness is that their effects are often temporary, and over-exertion of said Quirk usually leads to negative repercussions on the user's behalf. Transformation Quirks seem to be the least-common type of Quirk.

Mutant Class
Mutant (異形) Quirks can have a wide variety of features and abilities depending on the individual, but the common similarity seems to be that these Quirks are a part of the user's physicality. As a result, these Quirks are always active, but generally allow the user the greatest degree of control.

Mutant Quirks cause the user to exhibit irregular features that generally have some sort of purpose to them. Whether it be bodily alteration (Dupli-Arms) or enhancing preexisting abilities (Engine) mutant Quirks even have the ability to channel certain aspects of their user through them similarly to emitter-type Quirks (Earphone Jack). While not necessarily a weakness, mutant Quirks cannot be turned off, and sometimes cause the user inconvenience due to their malformations (such is the case with Mashirao Ojiro and his Tail Quirk, which makes it difficult to sit or lay down).

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