Who says the Order and Empyrean existed during the time Decius changed sides? But say they did. Empyrean is a religion that would shelter political and war refugees. Just like a neutral country like Sweden did during the WW2, and still do today. My reasoning for him starting in Bannor is they are probably the first nation to get a standardized organized Army in the age of rebirth. Being forced into a war against the orcs early, and having combat experience from hell. Not to mention being led by an Organized leader already. To me Decius was probably a commander/general in the Bannor vs Orc war. Once that war settled down, and the Embers was formed, he wanted more enemies. The other generals wanted stability and to build up the Bannor civilization now that they finally had peace. In some way or another, Decius does something controversial at this point. Like leading a band of loyal soldiers to war against some sovereign empire without any ok from the above leadership at all. Trying to force a war which his leaders do not want. At some point Decius gets taken care of and has to flee. He finds home in the Nomaic Malakim. This might be pre-Varn. Or maybe early varn. They might still be nomadic, without permanent cities. For some reason, through his political and military prowess perhaps, he climbs through the ranks and gains a high seat of power. Eventually, he gets driven away from Malakim as well, and then finds a permanent home in Calabim, where they appreciate his deterministic warfare style. I would guess he becomes a good friend of Flauros and maybe a lover of Alexis for a while.