In the world of My Hero Academia, nearly everyone has some type of Quirk, a unique superpower that manifests at a young age and typically belongs to them and only them. While every Quirk in My Hero Academia is at least a little different, even when taking heredity into account, most Quirks do share some broad similarities, allowing them to be broken down into four basic categories. So what are these four categories, and what do Quirks in each of these categories look like?

The big classes of Quirks are called Emitter, Heteromorphic, and Transformation, and each describes a common variety of Quirk seen in the series. Additionally, there's a fourth category for those that don't quite fit one of the above three categories. Some Quirks also bridge the gap between these categories, technically fitting into two different categories. This is most commonly seen with Heteromorphic Quirks, as these affect one's appearance, but don't necessarily dictate how the Quirk works. Here's a breakdown of each category in detail:

4 Emitter Quirks

Todoroki surfing on his ice in MHA

The most common type of Quirk in the My Hero Academia universe are Emitter Quirks. If a Quirk controls, projects, or manipulates something on command, it falls into this category. "On command" is a key element here--in order to be an emitter Quirk, the user must be able to activate or deactivate their ability. That can mean it's turned on or off at will, like Ochaco Uraraka's Zero Gravity, or it can be activated under certain conditions, like Rikido Sato's Sugar Rush quirk, which can only be used if he's consumed a large amount of sugar. Abilities like Shota Aizawa's Erasure Quirk both functions as an Emitter Quirk and can stop others from using their own Emitter-type Quirks.

Individuals with Emitter quirks are generally also equipped with the ability to tolerate whatever their Quirk generates. For example, Mina Ashido's Acid Quirk can be dangerous to others, but her body is resistant to the acid's effects. This isn't universally true, however, and even their bodies may have limits. Enji Todoroki, AKA Endeavor, arranged what's called a "Quirk marriage" in order to have a child with greater resistance to the heat generated by his flame Quirk by marrying a woman with an ice Quirk. While the term "Emitter" might imply that these Quirks can be active at a distance, that isn't a requirement. Many Emitter-types can only activate their ability by making physical contact.

3 Heteromorphic Quirks

My hero academia Tokoyami Koji Shoji

Heteromorphic Quirks, also known less politely as "mutant-type" Quirks, are those that alter a person's body outside of standard human norms. This broad definition covers a huge variety of alterations. It may involve gaining animal-like traits, such as Tokoyami's bird head or Tsuyu Asui's frog tongue; grant new appendages like Ojiro's tail or Shoji's dupli-arms; or alter other properties of their body, like Toru Hagakure's invisibility. Unlike Emitter-type Quirks, Heteromorphic Quirks are always active and thus are immune to abilities that might disrupt their function. They may still have active effects, such as the shifting traits of Shoji's arms, but are ultimately defined by permanent changes to the user's body.

Another unique aspect of Heteromorphic Quirks is that the physical change is not only permanent but inheritable. For example, Tokoyami's Dark Shadow quirk is completely distinct from his bird-like appearance, which was simply inherited from one (or both) of his parents. Many students in My Hero Academia's Class 1-A have at least a bit of Heteromorphic Quirk in their background. "Heteromorphs," as they're known, predictably experience discrimination in society, requiring special clothes and accommodations for their bodily differences. As such, they are much more likely to enter relationships with others who have the same type of Quirk, as was the case for Asui's parents.

2 Transformation Quirks

My Hero Academia Kirishima Using His Quirk

The last major category of Quirks is the Transformation-type quirks. As the name implies, a person with a transformation Quirk is able to change their own body in some capacity, either as an uncontrollable response to an event or at will. The degree of transformation can vary extensively; some, like Kirishima's hardening Quirk, cause the body's traits to change without significantly altering their appearance. Others, like Mount Lady's gigantification or Himiko Toga's transformation, can radically change how they look. Transformation Quirks differ from heteromorphic quirks in that the change to appearance is always temporary, although the amount of time it lasts isn't necessarily limited.

Transformations might also require a catalyst or resource of some sort. Toga's transformation needs a sample of the blood from the person she intends to disguise herself as, while Fat Gum's fat absorption Quirk uses his body mass to absorb objects and energy, burning the fat off as it is used. Transformation quirks are often quite powerful in My Hero Academia, but come at a higher risk to the user, particularly in the case of those Quirks that rely on some kind of resource that may be fully consumed in battle. There is also the risk of the transformed attributes becoming injured, which can complicate the healing process in some situations.

1 "Other" Quirks

My Hero Academia's Principal Nezu.

Of course, no classification system is ever perfect, so there will always be some abilities that don't fit neatly into one of the aforementioned categories. These "other" Quirk types may have some qualities of multiple categories or be far enough outside the norm as to not match up at all. One obvious case is Principal Nezu, who might at first appear to simply be an individual with a Heteromorphic Quirk. However, Nezu's mouse-like appearance isn't because he's a human who resembles a mouse--it's because he really was a mouse who spontaneously developed a super-intelligence Quirk.

Aside from Quirks possessed by non-humans, Quirks that steal or gather the abilities of others, like One for All or All for One, might arguably belong here as well. As Quirks are passed down from generation to generation, youth have demonstrated more powerful abilities with fewer drawbacks as the inherited powers accumulate. Combination Quirks inherited from a hero's parents might also mix powers from two or even all three of the formal categories, making them harder to classify.

One's Quirk can determine a lot about their life, such as with the discrimination seen against Heteromorphic Quirk users, so these categories can actually be quite important. No matter what category of Quirk one has, it's still possible to become a hero, hence the wide array of Quirks seen at UA. All three of the major Quirk categories have their uses, after all. Overall, My Hero Academia does a fantastic job at showing what a world with such diverse powers on display would be like, and these Quirk categories form the basis for the world as it's seen.