Lifting the Tyranny out of part one, making it a whole setting rather than a one-book aside in a superhero universe.
It’s a Standard Scifi Setting but it’s happening above our heads right now.
Borrowing a lot from Flash Gordon and the like (obviously) as well as its modern-er equivalent Star Wars and the modern-people-in-space-opera hooks of Doctor Who, Farscape and Stargate. In a superhero universe it would play a lot like Marvel’s Starjammers or Annihilation.
Rules-wise I'd use a pulpy or slightly-superheroic system rather than a full-on supers game. I've played a 30s Flash-style Adventure! game before.
Like Flash and Dale and Crichton and O’Neil and Star-Lord, the PCs get to be genre-savvy about the setting, once they get over the culture shock, and the players find out about it with them.
In the depths of space, the armies of the Tyranny assemble to ravage and conquer another world. Dozens of species work as slaves in the depths of their black and purple starships, powered by chained black holes, and the scientific minds and strong backs of humanity will be a valuable prize to the Tyrant and his council of backstabbing advisors.
Opposing them is a rag-tag fleet of escapees, other strange alien beings, and long-lost travellers from Earth...
And at some point, the PC strong guy will end up in a gladiatorial arena fight with the Tyranny champion and/or a captured rebel hero.
So we have a wide variety of aliens on both sides - free, enslaved or employed by the Tyranny. The Tyrant and his main forces are probably generally humanoid to make them relatable, but humans are a rarity. Human PCs are an obvious option, but there’s room for aliens, cyborgs and robots and the like.
The Tyranny has backstabbing advisors to allow for multiple enemy factions, and there’s room for feuding potential allies, shifty neutrals like Space Pirates, and other threats like Psycho Robots and Ancient Chthonic Evils to join in as well.
I imagine the PCs crewing a beat-up little spaceship, flying hit-and-run missions against the Tyranny armada, piloted by Amelia Earhart.