In this universe, your soul acts as your energy/life force. When your soul runs out, so to speak, you simply die.
However, there are individuals that possess both an excess of energy/life force and the ability to control that excess. This ability--KNOWN OTHERWISE AS MAGIC (will get a better name)-- manifests itself most noticeably as strange coloured particles in a person's eyes. It is believed that the colour of the particles, is the colour of your soul. MMM SYMBOLISM
Anyways, BASICALLY MAGIC WORKS LIKE GENERIC VAGUE ENERGY BLASTS AHAHAHAH.
AND. UHM. IT SEEMS TO BE A RECESSIVE GENE YEAH. REALLY RARELY MANIFESTS, ALSO.
OH YEAH RIGHT.
The machine is able to run on souls, for souls are composed of pure energy. The current Order wants and values magical souls above all else, because they possess more energy than regular souls.