Legacy of the House of Haarlock.
Here be monsters
The Koronus Expanse is the name given by Imperial authorities to a dangerous unexplored region of the Halo Stars beyond the Calixis Sector. The Expanse is accessed through the Koronus Passage, a treacherous but navigable route through the great warp storms that bar passage to the Halo Stars beyond the way station of Port Wander.
As is true of the Calixis Sector itself, the Expanse was untouched by the God-Emperor’s Crusade many millennia ago—and so it is a realm of fearsome xenos, treasures beyond imagining, heathen worlds of men, and the echoes of ancient doom. The Koronus Expanse in the 41st Millennium is a scattered, partly explored region containing a few young colonies and vast natural wealth still barely exploited. Rogue Traders vie with one another for known resources, heedless of lives lost in the pursuit of riches, while a tentative attempt at Imperial colonisation follows in their wake.
Drawn by the flow of wealth, pirates and servants of the Dark Gods have also slipped into the Expanse, eager to cast destruction upon the works of the God-Emperor’s faithful, living by what they wrest from dead hands, while the Expanse itself holds many secrets and native inhabitants no less dangerous.