Board Thread:General Discussion/@comment-25814498-20150505201606/@comment-27459426-20160218142532

Pigzillion wrote: My theory is that aura is a state of matter in the Hunter x Hunter universe which humans(and other life forms, e.g., chimera ants) have evolved to produce and harness. They store extremely high levels of chemical energy in there bodies and convert this into aura when they deem it to be necessary, Ren being the most obvious example of this. This state of matter would be very similar to plasma in that it is somewhat light, high energy and malleable, but is fairly low in temperature unlike plasma. It is clearly not just energy as aura has very clear effects on the environment and many of the characters in the show, even strong enough to shatter a rock wall in Uvo's case, and emission simply involves throwing a lump of aura at your opponent in hopes of making them "go boom" so to speak.

Since plasma is basically just a sea of highly charges electrons, Aura may be a sea of a different particle, one which doesn't release as much thermal energy and doesn't reflect or emit light in the visible spectrum. Therefore, transmutation may not be as complicated as we've made it out to be. By changing the positions of these particles they can take on different properties.

This kind of sounds like the explanation from Ajin where the "renound" expert was explaining about the black ghosts being energy and Ajin are humans that have evolved to produce this energy that is invisible to the naked eye.