Taking a stab at "rewriting" your idead - how about this...
In the Last Days of the Imperium, a minor marine chapter was tasked with a desperate mission to make contact with an edge-of-Tau-space Forgeworld and bring some sacred Terran technology back to turn the tide of the Last War. This Forgeworld had been out of contact with the Empire for several centuries due to fierce Warpstorms, but had recently been rediscovered by recently intercepted communications by the Adeptus Mechanicus.
However, upon landing on the Forgeworld, the marines discovered that it had (peacefully) been converted to a Tau allied world. Furthermore, shortly after the marine's arrival, the world was again shrouded in a fierce Warpstorm.
The marines engaged in a brief but bloody war with the entrenched Tau and native human population. However, the marines proved no match and those that were not killed were captured.
When the Tau Ethereal in charge of the newly acquired world learned that part of the marine's loyalty to the Imperium stemmed from hypnotic mind control implanted as part of their training, he was able to unravel it, freeing the marines of their dogmatic loyalty to the human empire.
With their eyes opened to the possibility of a life beyond the Imperium, some of the captured marines embraced Tau teachings and began to work with the now-native government.
Amid the cache of technology that was to be returned to Terra included research and a functional lab for reproducing marine geneseed. The new collective was able to unravel the technology and enact a working lab capable of producing new marines. Utilizing the native population, the marine chapter was able to replenish its losses - now loyal to the Tau planetary governor. Further, the Tau and human scienctists were able to reverse engineer some of the archaoetech to produced augmented Tau soldiers.
Several generations passed for the system, isolated by ferocious Warp Storms, preventing either Tau, marine or colonist from approaching or leaving the world.
When the storms finally abated, the combined hemongy was appalled at what they learned - in the interim, a great disaster had befall the galaxy, destroying both the Imperium and the Tau Empire. Worlds had been scoured clean, leaving little trace of the source of the disaster.
As scout ships scoured dead worlds to uncover what had occured, a strange portal was found on a barren world orbitting a sun that had been deliberately supernovaed. After experimentation, it was discovered the portal led into the past - several hundred years before the initial disaster had occured.
At the urging of its citizenry, the government approved a project to send its largest ship - the fully-loaded Space Marine barge - through the portal in a desperate attempt to discover the source of the ancient disaster, and if possible, to avert it.
Co-ordinating with the homeworld, that barge has now slipped into the past, with the hopes of preventing a dark future for the entire galaxy...
|