@Monarch Thinking about it, perhaps we could integrate @LloydTurquoise's Doctrinate? Could be how they possibly came into contact(unless the feds and docs rediscovered one another long ago)
Perhaps a distant independent colony of a federation-aligned species is attacked by the Imperium, when the call for help is sent out, a unsteady Federation recovering from a long war immediately responds with a small task force, causing tensions as the two factions make first contact.
@Monarch Same here :P Probably would have to be recent-ish, like say the last decade or a bit further. Probably not a shared history and more of the feds being vaguely aware of the Imperium.
I've been thinking of ideas for my explorer character. One such idea is a Mercenary who also is a War Vet who fought in the final years of the Xim War(or maybe First Contact War?).