Well, I have this group rp I was thinking of running that includes a few of these elements.

The Zodiac Interstellar cruise ship Scorpio is leaving a human colony world, carrying tourists, spies, ambassadors, archeologists, military personnel traveling on orders, honeymooners, etc. It's one of twelve ships on this circuit.

There is a reluctant unkillable assassin - it's said he's died a few times, only to pop up unexpectedly to kill whoever killed him. Nobody knows why he's on board the Scorpio.

There's a security detail guarding one of the cabins - nobody knows who's inside.

And then there's a girl who looks human but isn't (two hearts). She can't speak, she has no memories, and doesn't appear in any identity database. And despite top-notch security, nobody knows just how she got on board.

One of the stops is an alien refugee colony, stranded during a decade long war until rediscovered by the first humans to make it out that far. Oddly enough, they have a statue of a human next to a canal that he led the construction on, years before the colony was discovered.