(last updated: 12/28/17)
Psionic energy is a rare peculiarity, a kind of sideways analogue to chi in the view of even the most studied fighting scholars. However, no matter how often they are confused, the difference between Chi energy and Psionic energy could not in fact be any greater. While Chi energy represents the flow of energy through the world and the life force of a person, Psionic energy is specific to sentient beings, and is the closest thing most people have to a soul.
Psi is not well known in the world, and tends to be discovered and re-discovered by people with natural aptitude for harnessing it or finding others who can harness it. As a result, much like Chi has historically been referred to by several names, so too has Psi, being referred to as demonic energy, psionic energy, psychic energy, soul power or even, most famously, Psycho Power.
Much like all people have chi energy naturally, all people have psionic energy naturally. The primary difference is, psionic energy usually exists in much smaller quantities in a person. Additionally, psionic energy is much more unfocused than chi energy is, owing to the natural confusion a person experiences over their role in life. It takes great training, focus, or a singular galvanizing event to polarize a person's psi to the point where it can be used at all.
Psi, when channeled, tends to be naturally flashy and colorful compared to chi. Like chi, it can also have a natural disposition, however unlike chi, it cannot replicate natural elements. Most psionic energy tends to replicate the emotions of the user, such as pure evil, or love. However, more bizarre constructs ad dispositions are also possible when harnessing psionic power.
While psionic energy primarily deals with the energy of the mind and soul and chi deals with the energy of the world and the body, there is some noticeable overlap in the two when it comes to feats that affect the physical world. Namely, telekinesis, or the power to invisibly lift, push, crush or manipulate objects, is achievable by either psionic power or chi, though any noticeable and grandiose effects require a great quantity of either, and very fine effects require an extreme competency and skill with either.
Psionic energy typically requires less competency than some other talents to achieve minor feats, due to the events or training required just to harness small amounts of it to start with. At lower competencies, psionic energy typically has broad effects over the mind--being able to make minor suggestions, or insert the beginnings of ideas into the minds of others is common, as is some forms of minor mind reading.
At very high competency, Psi can be used to read minds over great distances. Full blown telepathy is possible, as is finely controlled or vastly destructive feats of telekinesis. Flying outright is also possible, but many of even the strongest psychics do not typically use more than one or two of these feats--one would have to be beyond a master, and sacrifice something very great indeed to achieve the focus needed to perform these feats in multiples.