The Ethric Mind, or Tatsuonga, is an entity formed out of the power of Fab'rasi that dwells within The Source. Full-blooded Arkn and Dekn (as well as half-breeds, Risen, and even Humans) make contact with it in order to practice various forms of magic.
Origin
After the creation of Universe X, the Hethe Fabr'asi took over The Source: a split in the former (rebooted) .Reality core that had been used to create a connection between the base of .Mainframe and the universe on top of it. Within this split, Fab'ras expelled the last of its power, creating an entity (or essence) of sorts. This being was called Tatsuonga. As no mortal beings have access to the Tatsuonga, its existence and role in magic is known only from the writings of Jacques (and is still regarded by some as a myth).
Function
The Tatsuonga releases a form of energy known as Ethri (which is allegedly its own life-force). Most sentient beings are able to tap into this energy in order to "prime" sigils; this is accomplished by focusing thoughts of one's intent towards the Ethric Mind, similar to praying. Arkn and Risen can charge sigils directly by channeling the Ethri in their blood; half-breed Arkn, Dekn blooded individuals, and Humans, however, cannot channel Ethri directly, and must use an external charge to power the sigil.