"It would be better for a man to die screaming in the jaws of the Tyranid and know release into the Emperor's grace, than to die easy in his bed on this cold world: for here, the souls of the dead hunger for company."
- —Malin Grey, Psyker Primaris, Special Inquisitorial Taskforce
Vanity -- as it has long been known -- is a barren, radioactive, and haunted wasteland of shattered hive cities and fallen grandeur.
During the ancient Jericho Sector's Age of Shadow, the prideful and fractious rulers of Corulsiem were among the first to fall to internal division and strife. Its hive cities erupted into a savage civil war, which quickly escalated to the use of forbidden atomic weapons, rendering the planet into a lifeless, cinder-shrouded carcass of a world.
For many centuries afterwards, Corulsiem was little more than a target for the most desperate or foolhardy of scavengers willing to brave its deadly, radioactive fallout-strewn wastes in search of spoils.
It became known more commonly by the name "Vanity" by those in the Jericho Reach, in reference to the hubris and folly of its former masters.
With the eruption of the Hadex Anomaly, Vanity's reputation grew even darker: engulfed for a time within the burgeoning Warp rift, legend has it that the tortured souls of Corulsiem's billions of dead rose up screaming.
Since then, Vanity has become legendary as a deadly, haunted place. These legends were proved to be lethal truth as this world became a second line in the war between the advancing Achilus Crusade and the Chaos forces of the Stigmartus; both have suffered at the hands of this world's spectral phenomena.
The fighting on Vanity has been both sporadic and brutal, with both sides trying and failing to gain the upper hand and use the system as a base for their own operations, or at least deny it to their enemies.
Owing to the extremely adverse conditions here, both sides have taken to deploying troops more likely to survive rather than more numerous fodder unlikely to live long enough to be tactically effective.
For the crusade forces, this means the deployment of elite Adeptus Astartes strike teams, while the Stigmartus has formed its favoured forces from twisted mutants well-suited to operate on the poisoned world, backed by witches and with deadly contingents of the Traitor Legions to lead them.
- Deathwatch: Core Rulebook (RPG), pp. 347-348