So in the best case:

Playing an OW soldiers, who in a mission saw too much and therefore was recruited by the DH2 Inquisition.

After years of service and building up contacts and riches, he leaves the inquisition and gets an arch militant for a RT crew.

On a trip, he gets in contact with the ruinous powers and slowly is corrupted to become a renegate, that wants to join a black crusade.

In "Best case" scenario, said Rogue trader becomes an Inquisitor himself (Full circle). As such He mounts his own Crusade into the Koronus expanse to reclaim it as an Imperial sector! (Actually this would also work if He just stayed a RT. I would dearly like to see RT updated to the BC/OW rule set next!