Ki

Ki (気; pronounced "Kee"), also known as chi or simply energy (エネルギー, enerugī), is the force energy used by the Dragon Ball characters. This force also bears some realistic tendencies being that it is "used" in the real life martial arts, such as Kung Fu and Tai Chi.

Background Information
Ki is also known as "latent energy" or "fighting power." The term is the Japanese pronunciation of the Chinese term "Chi" (氣), which directly translates as "life force." This force is a tangible energy inside every living person, with its major focus being in the center of the body. By drawing it out, an individual is able to manipulate it and use it for performances outside the body. Ki can be used for many different techniques. It is necessary to increase one's ki to become strong, because there are physical limits to the strength of the body itself, in order to overcome that barrier. Usually, the more concentrated the masses are, the more time the user requires to draw it out by powering up. When fighters gather ki, they are able to gain enhanced strength, speed, endurance, and can increase the power of their attacks to inflict greater damage to opponents. Normally, the more the ki is increased, the harder it is to control, so ki control is also important.

Hero: The Guardian Smurf stories
Only a few characters possess such abilities in the HERO series, the first known character to possess this ability was Master Kai, who is an ancient and wise martial arts master, and the first character to possess the legendary Power Stones, as they contained his legendary Ki energy. Due to the sheer power contained within the stones, many have tried to get their hands on them in order to cause chaos and destruction, but he protected the stones using his Kai abilities.

He later decided to seal the stones away from the world, as he didn't want anyone to use them for evil and he went to go live in a different dimension.

Hero was the second character to possess such abilities, since he found the Power Stones as a young Smurfling, and due to its power being uncontrollable at the time, he almost killed his fellow Smurfling, Jokey. Which resulted in Papa Smurf exiling him, and he could only return if he learned to control his abilities. He was later found by Master Kai in the forest, who decided to take him back to his own dimension in order to train him.

Wonder is another character to possess such abilities, since she is the female counterpart of Hero, who was created through the Mirror Of Opposition.

Hero's two daughters from separate marriages also possess these abilities.