Ki

"You call your power religious devotion. I call it "Ki". It's the same thing."

- Gouken to Dhalsim, Super Street Fighter IV

Ki (気), sometimes referred to as chakra or chi (the latter being modeled after its Mandarin/pinyin reading), is a form of energy that appears in the Street Fighter series.

Description
Ki is a preternatural and esoteric form of energy that is said to be found in all things. Within living beings, ki can be wielded and harnessed via martial arts and other forms of physical activity, as well as specific exercises. Ki can also be quantified as the strength and build of one's body, along with health, finesse, and muscle.

Many fighters in the series are seen wielding this power in their attacks, manifesting in projectiles and attack moves that are engulfed in energy.

Manifestation
Ki can take on a neutral form of energy, but as mentioned in the backstory of Urien, it is said that the user's own ki can take on elements one is more sympathetic with; as such, various elemental energies like flame and electricity are seen.

According to supplementary materials, its temperature throughout the series is also said to vary upon one's disposition and internal motives as well, regardless of one's manifestations; those who are motivated by negative emotions such as Akuma are said to have cold ki, those who fight with extroverted passion and a sense of justice like Chun-Li are said to have lukewarm ki, those who fight for the sake of improvement and justifying their need for combat like Oro are said to have warm ki, and those who use Psycho Power are said to have blazing hot ki, due to how the negative ki redirected but without anywhere to direct itself to manifest by the Psycho Drive's mechanics, becomes extremely erratic due to it being stored.

Throughout later series, especially in Street Fighter IV and Street Fighter V, ki is often depicted in the ink like motions and waves thematically seen in visuals. The new mechanic featured in SFV, the V-Trigger, is likely a new mechanic focusing on how one's ki manifests when they fight at their fullest state.

Character Ki Manifestations

 * Ryu: Light, Wind, Fire, Electricity and Power of Nothingness - The first time Ryu used elemental properties on his moves was in Super Street Fighter II's Shakunetsu Hadouken. Although it was not until Street Fighter III that Ryu gained an official affinity, he was given the electrical element in its fullest form in the lighthearted parody series Super Gem Fighter Mini Mix. He mainly manifests this through the Denjin Hadoken; Street Fighter V gives him the V-Trigger Denjin Renki, which charges his fists with a static aura. To a lesser extent, his ki has also shown to manifest in various other varieties. His ki is considered naturally warm.
 * Evil Ryu: Darkness, Fire, Electricity and Satsui no Hado
 * Ken: Light, Electricity and Fire - Ken can be considered the one of the first to have a manifestation series wise, seeing it manifest in his variation of the Shoryuken and the Shoryureppa. Crossover series depict this varied, but the Marvel vs. Capcom games sees his a greater majority of all his super attacks burst into flames. In Street Fighter X Tekken, his Shippu Jinraikyaku is inbued by lightnings.
 * Violent Ken: Darkness, Fire and Psycho Power
 * Chun-Li: Light, Wind and Water - Her ki has always manifested at its most basic form, and as a flowing light blue energy. Her Renkiko V-Trigger's dynamics subtly acts akin to water in motion.
 * Dhalsim: Faith and Fire - Though his training and grasp of spiritual metaphysics lie in that of another school, Gouken reveals a bit of interconnected truth in how Yoga and the concepts of prana, chakra, and kundalini share traits with the thought of ki. Though his flames are perceived as real, they are the result of spiritual works in that they are real if one thinks them to truly be.
 * Sakura: Light
 * Sean: Light
 * Alex: Light
 * Guile: Wind and Light
 * Nash: Wind and Light
 * Shadow: Wind, Light and Psycho Power
 * Sagat: Light and Fire
 * Dee Jay: Sound and Wind - With his love of fighting and dance, he is physically fit to both dance and thrash about. His Air Slasher is also said to move at the rate of the speed of sound, literally carrying whatever noise and audial media happens to be made in his surroundings, and amplifies it on contact to his target. His ki is considered lukewarm due to his love of fighting.
 * Blanka: Electricity
 * Fei Long: Fire
 * Cody: Wind
 * F.A.N.G: Poison
 * Abel: Wind
 * Zangief: Light
 * Rashid: Wind
 * Laura: Electricity
 * Ibuki: Light
 * Dudley: Wind
 * Dan: Light
 * Decapre: Darkness and Psycho Power
 * Rose: Soul Power
 * M. Bison: Darkness and Psycho Power
 * Ingrid: Light and Soul Power
 * Remy: Light - His wielding of light based ki is rather unique, in that his disposition, being cool, and hence negative, has also seemingly melded into his own flow. It appears as an icy aqua and white ki.
 * Yun: Wind
 * Yang: Light and Wind
 * Gen: Power of Nothingness and Satsui no Hado
 * Oro: Light and Jindan - Having mastered Senjutsu, the dynamics which dictate ki and are studied deeply by the martial art are refined greatly to balanced but potent proportions. This in turn creates what is known in Taoist lore as Jindan, being the literal golden elixir said to bring about immortality and legendary powers attributed to xian. Oro has attained Jindan within his being, and his abilities are nevertheless showcased; from superhuman strength to his limits to give his opponents a fighting chance. Manifesting as light is likely his choice of preference, as he can even manisfest an imitation of the Satsui no Hado.
 * Gouken: Light, Electricity and Power of Nothingness
 * Akuma: Darkness, Fire, Electricity and Satsui no Hado
 * Shin Akuma: Darkness, Fire and Satsui no Hado
 * Oni: Darkness, Fire, Electricity and Satsui no Hado
 * Necalli: Darkness
 * Urien: Earth, Metal and Electricity
 * Gill: Light, Cold and Heat
 * Juri: Light and Darkness
 * Seth: Light and Darkness (Tanden Engine)
 * Kolin: Cold
 * Ed: Darkness and Psycho Power
 * Menat: Soul Power

Forms of Ki

 * Satsui no Hado
 * Chikara no Hado
 * Senjutsu
 * Mu no Ken
 * Psycho Power
 * Soul Power