Let me give it a shot, just to start the conversation off So let us see. I'll start by arranging them into a rough timeline.
- In the darkest recesses of space, the whispering dreams of a sleeping entity call out. A wise, but stagnant empire, answers the call, hoping to serve the entity in exchange for salvation from inevitable destruction.
- A huge spaceship is sent from Earth to colonize a distant world.
- Civilisation had reached a shining pinnacle of Art, Science, and Magic, but then a Stellar Event occurred, and now all the rules have changed.
- ]An arcane field of knowledge - long lost and forgotten by most - has resurfaced, throwing a civilization into chaos!
- An ancient empire rises and falls.
In my mental model, there's a colony ship sent out from Earth, two in fact, but we'll get to that. The first ship is a slower-than-light generational voyage...most likely undertaken with the assistance of biological stasis, and a rotating crew selected for awakening during the voyage just to make sure it's all running correctly. It takes ages.
But, as they're en-route, Earth enters a period of chaos and comes out of it having forgotten some history (like when and where colony ships were sent), but with startling new tech, like faster than light drives. They send another ship to the same planet...but despite being the second ship sent, it gets there MUCH quicker. Thus, we have set up a conflict...the new colonists are already inhabiting the planet when the old ones arrive.
To make things even more interesting, lets tie this 'period of chaos' in to the dreams of the sleeping entity. Perhaps what befell Earth was a supernatural event. The return of old gods, old powers. Perhaps the key to FTL transit is magic, or psionics, or similar tomfoolry. The foothold they establish on the new world...fleeing persecution and hatred on Earth maybe?...becomes a kind of 'fantasy kingdom' to all outside appearances. Exotic 'races' that were humans who transformed themselves to fit niches, or just because they wanted to. Technology limited by a magocracy who don't want their power challenged by machines.
Which leads us to...the 'civilization' that is threatened by a 'stellar event' (the arrival of the other ship) which brings back 'lost and forgotten arcane arts' (technology and technological skills long suppressed).
And the players in this game could then be sort of semi 'hard' sci fi original colonists, or the magical descendants of the second wave of colonists...whose arrival on the world is now so old that it's probably mythologized. And of course there's room for mysteriousness too. This alien planet might have life of its own...and what of the whispers of those old gods? Why did human beings choose this planet...twice? Coincidence? Was it just one of the few good ones close enough to reasonably reach?
Lots of possibilities.