While normal Energon provides the fuel that keeps the Transformers alive, Rarefied Energon is something more. In this form, it is the base material of all Transformer life. Rarefied Energon is the base of the Transformers' physical forms AND the stuff of which sparks are made. Rarefied Energon is also apparently of limited supply throughout the multiverse. If it all were to be used up, no more Transformer life would come into being. Given this, its protection is of vast importance to Primus, and he has tasked one of his Thirteen original Transformers with its protection.