We've all seen those awesome video games and movies and comics where people throw "Hadokens" and "Hamehameha" around like it's nothing. It's flashy, does a ludicrous amount of damage (including the surrounding landscape), and usually produces massive amounts of light. It's also often referred to as chi, but almost always only seen in battle.
Consider the following on how this "chi" magic system works:
Any person is able to use this mystical energy - pending on the persons ability to focus and move his body. In other words, this magic can be taught to anyone.
This energy is dependent on the person's mental strength, where mental strength represents will, intent, and concentration. A person that is extremely focused on doing something will have much more success compared to someone who's doing the same thing half halfheartedly.
The magic does not allow for "super strength" situations - For example, if the person would not normally be able to lift a boulder, the chi would not allow him to lift the boulder. If the person normally could punch with 50lbs of force, a "chi punch" would also only result in 50lbs of force applied to the target.
A person must grasp the overall concept of this "chi" system in order use it. (The concept to be grasped is irrelevant). As such, one usually does not "accidentally learn" chi. It's more likely that someone teaches you the proper concept and how to think about the chi in order for you to start managing and using it.
What it looks like:
Flashy light is disturbing to neighbors. Which is bad.
This chi is visible to the naked eye, usually visualized as a distorted section of air based the form of the intent. For example, a punch could be either a ball of chi flying through the air, or a longer tendril extending from the arm to target, depending on intent. A palm thrust could easily be as large as the cross section of a car, where as a finger thrust could be as sharp as a needle point.
How the chi is used:
This chi magic is often (for lack of a better word) "Activated" through martial arts; however, simply focusing on the principles of what is trying to be accomplished is enough. Consider the following situation:
As Chi master Charles walks down the street, he notices a teenager trying to open a door from a distance. He's clearly practicing how to use his chi, and is launching a furry of chi punches at the door, but it's not budging at all. Charles decides to show off a bit, and takes the place of the teen. Concentrating on his intent to twist the doorknob, he extends his hand and grasps the air. Bystanders stop and stare as a circle of distorted air grasps the doorknob and twists it in unison with Charles wrist turn. A slight chi push follows, and the door swing opens.
An advanced user such as Charlie was able to manipulate his chi to twist the doorknob and push instead of throwing brute force at the door. Taking this example, if the door were a well oiled 100 lbs door with a thick steel lock, even if the beginner might have been stronger physically than the advanced user, a advanced user grasped the concept better and could open the door, whereas the beginner would not have been able to make it budge.
But doesn't this all seem too perfect and convenient?
With any advantage there must be a drawback. Use of this magic does not drain actual physical strength - however, excessive use of this magic can cause irreversible brain damage in children, resulting in things including but not limited to: Alzheimers, ADHD, Memory loss (Short term and long term).
Here, children are defined as anyone younger than 18. As each person nears the age of 18, the use of this magic causes less damage, but becomes harder to learn to use. Once the person has passed the age of 20, he/she is free to use this magic with no side effects other than the mental exhaustion of continuously focusing on things. However, the younger the child is, the more damage the magic does.
It's well known that children absorb information and learn a lot better than grown adults - their minds are like sponges and aren't as saturated. While this magic can be drilled into adults, it's significantly harder than teaching it to children. Those who have been taught to use it from a young age use it much more effectively than those who learn it later. To give a sort of comparison between the early and late learners, those who learn it late (post 18 years old) are at most able to use chi at a 20% efficiency rate compared to those who learnt it earlier. Learning it before age 6 would give 100% efficiency rate at age 18 if practiced enough and trained properly.
Unfortunately, children also tend to not listen to adults. Once they learn it, we can't simply tell them "don't use it, it's bad for you", or explain why it's bad for them (if they're too young to understand). They'll probably abuse it for personal reasons such as entertainment, or for mislead young adults, fighting or stealing or whatnot.