Ki (気; pronounced "kee"), also known as chi or simply energy, 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.
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.
According to Akira Toriyama, ki is made up of three components: Genki (元気; lit. "Energy"), Yūki (勇気; lit. "Courage") and Shōki (正気; lit. "Mind"). Also, ki can be "positive" or "negative", depending on the user.
In the English version of the anime, the term ki is rarely used, usually referred to as "Spirit Energy" or "Energy" instead. However, it is referred to by name in video games, even in the English versions. It is called W in the NES game Dragon Ball 3: Gokuden. It is refered to as airbending in Dragonball Evolution.
Ki comes in a variety of colors. The most common color in the series is white; other colors include yellow, red, purple, orange, blue, green, pink, and black. These colors vary on the race, technique being used, species that the character is, and/or the purity of the user's heart. It can also resemble electrical sparks or even sparkles of light.
The term ki was first introduced by Master Mutaito in a filler Dragon Ball episode where Goku travels back in time and learns about ki. The first usage of it is seen when Master Roshi performs an energy blast called the Kamehameha in order to extinguish the fire on Fire Mountain: by drawing his ki energy into the palms of his hands, Roshi is able to expel an explosive mass of visible ki energy. This was the birth of the energy attacks in Dragon Ball.
Auras of ki radiate from the user when increasing the concentration of it inside their body. Warriors (excluding Androids) have a limit to the ki that their bodies can withstand, but the capacity for ki can be increased through mental and physical training. Some techniques (such as the Kaio-ken) rapidly increase the concentration of ki in the body, enabling the user to fight at a strength level that far exceeds their regular limits for a limited period of time. Auras can displace solid matter.
In the anime, auras are sometimes used for comical effect; for example, during the Garlic Jr. Saga, Goku's wife Chi-Chi angrily produces a red-colored (similar to the aura produced by the Kaio-ken) aura after being angered by Maron (Krillin's girlfriend); though it appeared similar to the Kaio-Ken, its red color was likely intended to comically represent Chi-Chi's anger.
In Dragon Ball Z: Budokai Tenkaichi 3, there are several Aura Charge Z-items that change the default color of a character's aura to a different one (for example, Aura Charge Red gives the character a red Kaio-ken-like aura) or grants an aura effect on characters (like Androids) who do not possess an aura. There is also the bio-electric aura produced by the Super Saiyan 2 and Super Saiyan 3 levels (and Cell as well). In the anime, lightning auras are sometimes placed randomly on various characters, regardless of their transformation or power level.
Main article: Transformation
Depending on their genetic inheritance, some beings are able to transform. However, not all beings are able to transform at will; in some instances, there must be certain environmental conditions required for their transformation (like moonlight for Great Ape transformations) or emotional upheaval (for Super Saiyans). By transforming, a person then acquires physical limits that somehow change the ones of their regular body. Effects of transformations usually include alterations in strength and ki capacity. Some other effects may include differences in speed and durability. The most common transformation is the Super Saiyan transformation, which is only accessible to certain Saiyans and Saiyan/Human hybrids. The negative aspect of most transformations is that the process itself consumes energy. The effect of energy loss when dealing with Super Saiyan transformation can be limited through training.
Transformation is not always intended for increasing abilities. Some beings are known to transform in order to limit their abilities rather than increasing them. An example of this is Frieza, who was first seen in a suppressed state, being that his fourth form was his original state, and the form that he is first seen in was actually a transformed one. Cell demonstrated a similar ability when he reverted to a larval state in order to fit in Future Trunks' Time Machine and save energy during the time that he had to wait for the Androids. Then there was Super Buu, who transformed into his original Kid Buu state after his counterpart was removed from his body.
Main article: Saiyan
Saiyans and their hybrid counterparts are naturally adept at using ki. They generally have no difficulty manipulating their energy, and have even evolved to have the ability to increase it numerous times in battle without much effort. This is much unlike Humans who usually spend themselves after the first increase. However, unlike Namekians, Saiyans don't seem to have a natural ability to detect ki by sensing ki signatures. That ability must be acquired through learning.
Main article: Namekian
Although Namekians are generally not as strong as Saiyans, their ability to use ki is as good as that of Saiyans. Namekians use ki in more mystical ways than Saiyans do, but use it in the same manner when fighting. Namekians also are able to naturally detect ki energy by sensing the power of it. Namekians also are able to sense the "evil" in a being's ki.
Main article: Human It is very uncommon to see an Earthling who uses ki energy, though several humans have been shown to acquire full mastery of the art. Among those are Yamcha, Tien Shinhan, Krillin, Chiaotzu and Master Roshi. Another, lesser adept human is Videl, who was taught basic flight from Gohan (she can fly, but she is no match for Z Fighters). Other users include Spopovich, Yamu, and Olibu (although Spopovich and Yamu were Majins and do not really count, and Olibu may have learned the art in the Other World). Humans also have a natural disposition to detect the concentration of ki that their opponents possess (though the ability has to be learned).
Due to their unnatural occurrences and mainly stemming from Mr. Satan's claims, around Age 767-Age 774, Earthlings would come to believe that all ki-based techniques are just tricks. In the events leading up to the computer game Dragon Ball Online, in Age 804, Gohan wrote a book called "Groundbreaking Science" which reveals his studies on advanced martial arts and ki control. As of Age 1000, many Humans fight using ki attacks; including powering up and raising their ki, producing energy waves and spheres, discs, and self-destruction techniques. The Kikoukenjutsu Sword School, founded by Trunks and Goten to educate Earth's newer generation of warriors, focuses on the principle of channeling ki energy through swords. Tien's newly re-established New Crane School focuses on high spiritual damages; in some instances, techniques where the user must sacrifice health to produce the powerful attacks. All playable races, including Humans, can use the Kaio-ken technique, which constantly drains the user's HP (health) and EP (ki).
Main article: Android Androids generally have an unnatural source of ki, so sometimes their ki capacity is unlimited. Most of the time, because it is unnatural, it is unable to be detected by sensing. Conversely, most Androids are not able to detect other sources of ki by sensing. Instead, they must have special devices to do that. Some Androids can absorb other forms of ki, as well as energy from other life forms.
Androids like #17 and #18 are human, yet cybernetic modifications to their bodies have given them a near limitless supply of ki.
Main article: Kai
A Kai's energy is mostly invisible. Two Kais have been seen using invisible blasts; the first one was King Kai, who used his invisible ki to assist his pupils in his training. The second was the Supreme Kai, who thrust his hand forward and caused what appeared to be a gust of wind to blow at Majin Buu, having no effect whatsoever.
Extraterrestrial, monstrous creatures, and demons are also sometimes able to use ki.