Deep within The Warp there is pocket of stability. Named the Immaterium Sargassum by the first explorers to find it millennia ago, this giant swirling vortex within the currents of the Empyrean has collected bits of debris that have chanced by. Over the tens of thousands of years that ships from realspace have traveled the warp, everything from giant fortress ships down to single-occupant shuttlecraft, even the dust and debris that they left behind has entered the Sargassum and never left.
Orbiting The Filament is a titanic conglomeration of ships and other debris known as The Gyre. Ships, asteroids, even ancient space colonies are all crushed together here. A huge, planet-sized bubble of atmosphere has even formed as gas from realspace has accumulated. Lost survivors have made their homes here, scavenging from the strata of ancient hulks that form The Gyre. Entire ecologies of life have made their home within The Gyre, both nourished and warped by the energy from The Filament and the ever-changing atmosphere that permeates The Gyre. New debris is constantly being added to The Gyre as it drifts inwards from the Warp. Ships from thousands of years ago drift in as if no time has passed (and for indeed none has passed for their inhabitants). Technology from all eras coexist together forming a strange, potentially rich resource for those who call The Gyre their home.
Far out from the center there are other smaller collections of matter, each whirling in minor eddies of Warp energy, themselves orbiting the gigantic central core. The space between is alive with Warp energy...and the life that has arrived and evolved in the spaces between the gyres. Even some spacecraft have maintained enough integrity to continue to navigate The Sargassum (if not escape it)...or been engineered by the inhabitants of The Sargassum to travel from gyre to gyre.
The Gyre is, naturally, rife with conflict. Ancient tribes who have lived their for millennia contend with newcomers for the limited resources of The Gyre. Ancient horrors from the Warp itself manifest within The Gyre, eager to feast on the rare psychic emanations of the life that clings to the rare accretion of matter within The Warp. Raiders make their bases within still functional spacecraft, or within smaller gyres, leaving only to pillage what they can from other survivors. Some inhabitants of The Sargassum have even arrived with purpose, somehow becoming aware of existence, seeking its mysteries for unknown reasons.
This is The Gyre. This the Immaterium Sargassum.
Now. A mysterious ship has entered the Sargassum. Under power and clearly able to navigate within the Sargassum, it travels towards the central gyre. Is it a way for survivors to finally leave The Gyre? A source for new technology? Or just full of energy to be siphoned off. Groups from across The Sargassum rush to this mysterious and disruptive newcomer, each with their own motivations, and each willing to fight and defeat the others to claim their prize.