A world on the rimward edge of the Stygies sub-sector and far from any useful routes, Nurn Delta has never truly been counted amongst its worlds. So far as the houses of Askellon are concerned, it is a world of wind-blasted plains populated by savages, barely able to speak and concerned only with braining one another with large rocks. This combination of isolation, apparent lack of natural resources, and the utterly regressed state of the native human population means that few Askellian ships ever visit it. Vessels from elsewhere entirely visit it, however, drawn there for unique reasons of their own.
Once per generation, a warship bearing livery of brightest sky and purest cloud arrives by way of Warp routes not known to any of Askellon’s Navigator Clans. Small parties of huge warriors suddenly appear on the surface at a time and place foretold at the height of the previous visitation. Their arrival heralds a period of trials, wherein the chosen sons of the numerous tribes set aside their rivalries and compete against one another for the favour of the sky warriors. These contests are waged until only one warrior from each tribe remains. From these, the visitors select those they judge worthy to begin the process of training and transformation that will, in a small fraction of instances, lead to the initiation of a new brother in their ranks.
It is a matter of great anticipation amongst the tribes when the foretold time is almost upon them. Many hold that the wait is itself a test of faith, and the tribes must prove themselves worthy by engaging one another in renewed hostilities. As the time of trials approaches, the tension nears a fever pitch that will only be relieved when at last the sky warriors return to Nurn Delta.