Souls

As described by the PDR official guide, they are the physical states of energy that give life to various beings, therefore, acting as a power source for a body. Another function for souls is communicating to the brain while this sends memories to them. As seen several times in the comic, souls come in diverse colors depending on the race, however, in the humans case, they ome in any color. Depending on the race, also souls contain different properties and energy

Usage:
The general usage for Souls isn't very well-known, although, it has been stated, more often by Cultists and Demons, that souls are tradable. As PDR Guy sells his soul in the beginning of the comic, which isn't really shown to have affected his life much. The only two other people shown to have sold their souls are Stylish Cult Guy and Mercenary Human, the former of which actually had his soul destroyed, which was shown to turn him into a mentally unstable wreck, it's later shown that Souls can inhabit other bodies from their own, but how it can be worked with varies from species to species.