The Unum are a slightly more advanced version of our own medieval period. Their planet contains a large quantity of rare unmined ore that would be invaluable in the war effort. More importantly they are the only known species that can master all four matter elements equally.
Originally these plant like creatures were known as the Cleminca (Clem-in-cha) though a planetary cataclysm split their species into two. The Hornace evolved with limited water and are far removed from the water thriving Boava.