Ki

Ki, or qi, is an important term and element in the Street Fighter series.

Description
Similar to its real life counterpart, ki is a preternatural and esoteric form of energy that is said to be found in all things. Amongst living beings, ki is shown in the series to be capable of being wielded and harnessed as an energy that flows through the body. Martial Arts and physical activity, as well as specific exercises, related or not through specific martial arts, is shown and said to exercise harnessing this flow of energy.

While not exactly referenced to per say, many fighters in the Street Fighter series are seen wielding this power in their attacks, manifesting in projectiles and attacks engulfed in energy. Although there are plenty of attacks that do not exude ki from their execution, ki is also considered through the strength and build of one's body, as the health, finesse, and muscle of oneself can be seen as having a lot of good ki.

Manifestation
Ki in the series has been seen to take on not just a neutral form of energy, but also ones with heat and flame, to being charged with electricity.

As mentioned in the backstory of Urien, it is said that one's own ki can take on elements one is more sympathetic with; Urien is said to have merged his own flow with the elements of the earth, metal, and electricity, while Gill is said to have control over the cold and heat. Seth is also shown to be able to harness the powers of light and darkness. It is unknown what other kinds of elements one's own flow of ki can merge with in the series.

A malevolent form of ki, the Satsui no Hado, is mentioned as the result of ki being steeped in the darker aspects of human instinct and the drive for destruction.