From the Worlds In My Head: The Silmn are spirits coalesced into living crystalline bodies. To the layman they appear as humans made from frosted glass, and are by most accounts beautiful. The galactic wars of the last millennium have left their territory vastly reduced in the onslaught of the Nathi and the First Ones, but still they fight.
The Eidolon Warriors of the Silmn, here shown, are the new wave of soldiery - uploading themselves body and spirit into armored battlesuits of reinforced crystal and bonemetal. These suits provide both greater effectiveness on the battlefield, but also a (small) chance for a casualty to transmit himself bodily to the HQ positions and survive the battle.
The vehicles operate similarly, though they do contain a rudimentary cockpit as well.