You are asking the wrong person to to define the mystical Ki. I feel that it is a coodernation of the mind and body. I teach it as such and if you look at the first few posts I give a longer definiton.
I think that some people get involved in Aki arts for the wrong reason, that is to get this super mystical power and astound thier friends with its magical ability. Find a good teacher train consistently and practice the whole art, mentally as well as physically.