We need to settle on a setting and theme. In an effort to avoid any known Intellectual Property, it'd be best if we design our own universe (Though, we can take a great deal of inspiration from various Sci-Fi sources...)
That said, I have two suggestions from my portfolio - and one from the modern world.
Suggestion 1 - Beyond Infinity: BI was a series I ran many many moons ago, set in a universe where gods, and mythological creatures roamed free. Zeus was the king of the planet Olympus and ruled the Alliance of Light for millenia, protecting it from the Shadow of Hades, and the shadow (literal shadow people) of the Hadin.
Suggestion 2 - A world I'm currently writing a book about: I'm writing a Novel based in a Tolkein-like fantasy world, but some 400 years in the future. So it's Lord of the Rings, in space.
Suggestion 3 - Space Force: We can use the modern world as a template, keep things Human within the base game, and explore the militarization of space some 80 years or so from now.
Personally, I feel Suggestion 3 is the most scalable canvas of the three suggestions, allowing for the most modability, without stepping on any possible IP's toes. - but, I'm open to other suggestions and ideas
Bottom line, we need a theme!