Author's Note: Hello, all. Welcome to A Crash Course to Quriks! The goal of this guide is to give an idea of how to make a Quirk that blends seemlessly into the My Hero Academia canon. I hope this will help!

Disclaimer: This is a guide to help create a Quirk that fits in with the My Hero Academia universe, not a gauge of whether an original character is good. A character with a Quirk that bends and breaks these guidelines is not necessarily bad. Similarly, a character whose Quirk does follow the rules isn't necessarily good.

The Basic Information:

- A Quirk is a physiological difference, which can be like a superpower. It can also be something rather useless, like a pair of horns. Unlike superpowers from some other media, they are rather biological in nature. Some have canon pseudo-scientific explanations, like how Bakugo produces nitroglycerin in his palms to create his explosions.

- In the time the story takes place, the percentage of the population that has a Quirk has risen to a whopping eighty percent. Judging by how unusual Izuku's Quirklessness was treated, most of the remaining twenty percent is likely comprised of older individuals. If a story takes place earlier, the percentage of people with Quriks will be lower.

- Quirks are inherited. Children are expected to have the Quirk of one of their parents or a combination of both of them. It is possible for a child to have a Quirk that resembles neither of the parents', but instances of that are noted to be extremely rare. Additionally, two people with Quirks can have a child without, and a child of Quirkless parents can have a Quirk.

- Physical differences are not uncommon. Typically, the unusual traits are associated with the Quirk's function or theme. However, this isn't necessarily the case. Tokoyami's Dark Shadow, for example, has little to do with his bird head.

- There are three known Quirk classifications: Mutant, Emitter, and Transformation. An exact definition has not been canonically provided, so the following descriptions are educated guesses. Mutant Quirks are a permanent physical change, something that cannot be turned on or off. Emitter Quirks produce a substance or effect when activated. Transformation Quirks allow the user to alter all or part of their body in a certain way. Some canon Quirks seem to have traits from multiple categories.

What is Overpowered?

Quirks vary wildly in power. At one end of the spectrum, there are powerful Quirks like Bakugou's Explosions and Todoroki's Fire and Ice. At the other end, there's Ojirou and his tail.

Most original Quirks seem to be on the high end of the scale. And, as powerful Quirks do exist in the universe, there is, theoretically nothing wrong with them. Do keep in mind that the My Hero Academia cast has a variety of power levels. If there are many original characters, it would be more natural to preserve that variety. Those who indulge in the guilty pleasure of SYOCs might consider that the host wouldn't want twenty Bakugou or Todoroki-powered characters.

With that said, there are some things that can make a Quirk come off as overpowered or a poor fit for the universe.

Multiple Quirks (aka. The Todoroki Conundrum):

Todoroki exists. With both fire and ice powers, he's one of the most powerful students in the series. That does not mean that smashing together multiple unrelated Quirks is a great idea.

Instead, consider making a singular Quirk. Said Quirk may have multiple abilities, but said abilities are all easily related to each other. Fire and ice, in a way, are kind of related. They both have to do with temperature. Smashing together, say, telepathy and super strength is going to look pretty weird. A suggested rule of thumb, if a Quirk cannot be described by a sensible word or short phrase, it will probably come off as Quirks smashed together.

Special Quirks:

A special Quirk is, well, special. In-story, it's likely lauded as rare or special, often to "justify" how powerful it is. Sometimes, these Quirks break the rules of what a Quirk usually is. Instead of being a physiological difference, the special Quirk might be magic/spirit/Qi-based, gained from an experiment, be multiple Quirks (see section from earlier). Sometimes, it's so different from what a Quirk is that it can hardly be called a Quirk anymore.

Special Quirks aren't necessarily bad. In a way, One for All can be considered a special Quirk, seeing how it is passed from generation to generation, unheard of for Quirks, and seems to have some spirit-like properties that are still not fully understood. However, it has a lot of plot surrounding it, like the fight between it and All for One, as well as Izuku's struggle to use and accept it.

Overall, special Quriks require an extremely good, plot-important reason to exist. Otherwise, you're probably better off giving them a Quirk that fits in the canon universe. For example, does a character really need to magically summon fire from Hell? Why not have them produce fire from a combustion reaction that happens in their palms instead?

Story-Breaker:

A story-breaker will be defined as a Quirk that can easily solve whatever conflict the character faces. Story-breaker abilities are harmful to a story because they prevent the character from facing any real challenge. If you find that your story has no tension unless your character constantly forgets about their powers, acts incompetently, becomes incapacitated, or faces enemies with power levels dialed so high that their peers have no hope of standing up to them, then that can be an indication of a story-breaker.

Time manipulation, teleportation, mind control... quite a few abilities can become story-breakers. Let's look at Aizawa's Quirk, Erasure. It has several limitations, including deactivation when he blinks and being unable to erase the Quirk of someone he cannot directly see. Without those limitations, Erasure could easily become a story breaker because it would end fights all too easily. See the "Limitations" section for examples of how you can prevent a power from becoming a story-breaker

Strength without Practice:

Pro heroes have spent years honing their Quirk. Even with a powerful Quirk, a character cannot hope to be at their level without putting any effort into training their Quirk. Regardless of what their Quirk is, a character is going to look pretty overpowered if an inexperienced character easily beats a villain that's been causing trouble for the pros.

Notably, the canon characters don't become stronger by gaining new powers; rather, they learn new tricks they can do with the power they have. Especially if you're writing a hero student character, give them aspects of their Quirk that they need to work on. Watching a character grow is the fun part of a story.

Limitations:

Quirks have limits, a fact that has been emphasized throughout the series. This makes them different from superpowers seen in a lot of other media. Generally, the greater the power, or the more potential it has to solve problems, the greater the limitations are expected to be. While training and support equipment can help characters improve their power output and reduce the effects of these limitations, they will still exist. The following are just a few types of weaknesses and limitations.

- Overuse. One of the most common Quirk weaknesses. Quirks can cause undesirable, potentially damaging, effects when pushed to their limit, not unlike how a muscle can be strained from overuse. These effects tend to be thematically related to the Quirk itself. For example, Todoroki can get frostbite from overusing his ice powers, and Ochako gets motion sickness from her zero-gravity Quirk.

Sometimes, a special, extra-powerful technique that a character uses can trigger these weaknesses. Iida's Recipro-Burst, which gives him a great speed boost at the cost of stalling his engines when it is over, is a good example of this.

As a side note, fainting when the danger has conveniently passed and waking up with no issues is not a great limitation. Neither is coughing up blood and being completely fine afterward. Seriously, coughing up blood is a sign of a severe medical problem.

- Environment. A Quirk's strength and usefulness might be affected by the environment around the user. A couple of examples are Tokoyami's Dark Shadow, which has a strength-control tradeoff depending on the amount of light present, and Mount Lady's Gigantification, which ill suited for crowded cities (not that it stops her). Additionally, in the My Hero Academia world, collateral damage is also taken seriously, meaning that those with destructive Quirks have to be extra aware of their surroundings.

- Activation. Another common limitation. Some Quirks aren't activated by will alone; a condition must be met. Shinso cannot brainwash people unless they verbally respond to him. Ochako and Shigaraki both need to touch their targets with all five fingertips in order to use their Quirks. Sato must consume sugar in order to use his super strength.

- Control. A user might have aspects of their Quirk that they cannot control. Again, Ochako is an example. Her Quirk activates whenever all five fingertips touch an object, whether she wants to activate it or not. She takes precautions, like keeping her pinkies raised when holding items and sleeping with mittens on.

- Range/Maximum. A Quirk's effect may only work within an X meter radius, or they may be limited to affecting objects with weight less than X kilograms. Or similar. These limitations tend to be softer, meaning that a character may be able to raise them with proper training.

Again, that isn't every possible limitation out there. Whatever limitations you choose, pick some you're willing to write consistently.

Quirk Brainstorming Ideas:

- Base a Quirk off of an item. Hell, there are Quirks inspired by earbuds and tape!

- Base a Quirk off a body part.

- Take a common superpower and deconstruct it.

- Base a Quirk off of an animal.

- Give a character a Quirk that perfectly describes their personality.

- Give a character a Quirk related to their interests

- Use a random word generator