A Quirk, also known as a Meta Ability by the Meta Liberation Army, is a special, superhuman ability an individual can possess. Quirks are generally unique to their user, and are classified in multiple categories.The first person to manifest a Quirk was a newborn baby in the city of Qingqing, 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. The cause of the Quirk phenomenon is unknown, it has been theorized that the spread of a virus carried by mice had brought about their development. Currently, around 80% of the world population possesses a Quirk. Quirksare inherited genetically through what appears to be endelian inheritance and typically manifest in children by the age of four at the latest. Children will either manifest one of their parent's Quirksb or a new composite Quirk formed by the fusion of the two. This composite Quirk may sometimes give the appearance of the person having two separate Quirks, such as Shoto Todoroki's Half-Cold Half-Hot. Much more rarely, in the case of Eri's Rewind and Tomura Shigaraki's Decay, a child may manifest a Quirk that is entirely unrelated to their genetic lineage, akin to a mutation.
Emitter type Quirks have the ability to either release certain substances, or alter materials around them in certain ways. Emitter-type Quirks usually require a conscious effort to activate (such as Electrification, Explosion, and Half-Cold Half-Hot), 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 use, others does not.
Transformation type Quirks 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 (Hardening, Gigantification) or perhaps adding new features to the body altogether (Tool Arms). Transformation-type Quirks generally affect the user exclusively, the only known exceptions being the Meatball Quirk.
Mutant type Quirks can have a wide variety of features and abilities depending on the individual. Generally, Mutant-type Quirks are associated with the user's physicality (mutations). As a result, Mutant Quirks are passively active and, at a glance, are the most identifiable.Mutant-type Quirks create bodily structures that bestow the user more complex abilities that Emitter and Transformation Quirks cannot safely provide. So that is all about mutant type quirk.