Ki (気; pronounced "kee") is the force energy used by the Dragon Ball/Z/GT characters. This force also bears some realistic tendencies being that it is used in the real life martial arts such as Kung Fu or Tai Chi.
Ki is also known as "latent energy" or "fighting power". The term is the Japanese romanization of the Chinese term "Chi" (氣), which directly translates as "life force". This force is a tangible energy inside a living being, its major focus being in the center of the body. By drawing it out, a person is able to manipulate it and use it for performances outside the body. Ki can be used for many different techniques. Usually the more concentrated the masses are, the more time the user requires to draw it out (to "power up"). When a fighter gathers Ki, he or she is able to gain enhanced strength, speed, endurance, and can increase the power of their attacks to inflict greater damage to opponents.
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, or how (im)pure the being's heart is.
The term "Ki" was first introduced by Master Mutaito in a filler episode of Dragon Ball where Goku travels back in time and learns about Ki. Although it is unknown who originally discovered this inner energy in the Dragon Ball timeline, the first usage of it is seen when Master Roshi performed 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 was able to expel an explosive mass of visible ki energy. This was the birth of Dragon Ball energy attacks.
It is unknown whether or not the incantations (such as "Ka... me... ha... me... ha!") must actually be spoken for the attack to be performed, or if the incantations are anything more than glorified battle cries. Often, the Z Fighters and their enemies can perform attacks without saying anything, but there still exists the possibility that they are actually thinking the incantations, rather than saying them aloud.
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 tiring easily. This is much unlike Humans who usually spend themselves after the first increase. However, unlike Humans and 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 — if not more advanced than — 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 concentration 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, 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 don't 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).
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. But, also, most of them are not able to detect it by sensing either, instead they must have special devices to do that. Some Androids can absorb other forms of Ki.
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. Only two kais have ever been seen using it; 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.
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 also displace solid matter.
- Note: 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 (Kaio-ken like) 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 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.
- Note: In the anime, lightning auras are sometimes placed randomly on various characters, regardless of their transformation or power level.
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 commonly seen 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 then 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 Trunks' time machine and save energy during the time that he had to wait for the Androids. Then there was Buu, who transformed into his original Kid Buu state, after his counterpart was removed from his body.