Time has dissolved humanity. All that is left are the Arta's - soldier class clones - and the wars they wage across Orion. But, upon completing their tours, the Arta's retire to Incuso: a manufactured Valhalla where these warriors can die cumming.
Survive long enough, or absorb the right blood from the right Vower, and an Arta can acclimate to the air. No longer needing the filter, she can stop wearing the mask. Only a few have ever achieved this.