Ki is a form of magicke-like power employed by martial artists. It is a very rare talent used by only masters of the fighting arts.
While numerous systems of martial arts exist in EC's world, Ki uses short bursts of magicke to dramatically enhance the effects of these arts. In general, most of the modern schools descend from Asia, where civilization first discovered Ki and where it is culturally derived. To know Ki, a character must be either from or trained in one of these nations, or trained by a descendant of Ki masters from the region.
Ki uses a type of magicke that can be performed instantly without incantation, is concentrated in specific muscles and bones, and lasts for no more than an instant as well. Ki users are not sorcerors or mages. They are users of a very specific type of magicke-like force that enhances the fight potential of their bodies.
It takes years upon years to learn even the most basic of these techniques, and its secrets are extremely well-guarded. Nobody knows Ki who is not part of an elite school of martial arts, or under the training of a Ki Master or Teacher descending from a line of Ki mentors. Wild talents are even rarer in Ki than they are in standard magicke.
Another way of putting this is that while years of study in martial arts could potentially allow a character to fight as well as the best of UFC, Ki allows a character to fight like Bruce Lee, or an expert samurai, from fantastical movies. Expert Ki users often use this power to possess lightning-fast reflexes and supernatural speed, stamina and attack strength. Some use their Ki to become experts, also, in the use of weapons, however this almost never extends to firearms, owing to a bit of almost religious prejudice against their use.
Some noted Elysian users of Ki: