
Umbral Reaver |

Let's see. What must a void subtype have?
Does not need to breathe.
Immunity to vacuum pressure.
Immunity to low radiation (although Starfinder may ignore environmental radiation in space).
A fly speed that functions in a vacuum.
I don't think anything else is absolutely necessary, that I can think of right now.

Matthew Shelton |

As well a void creature might be void + cold; e.g. lives on airless or microatmospheric dwarf planets or moon Pluto-Charon, or one of the airless cold moons like Triton, or in the asteroid belt ...
Or it might be void + fire; e.g. loves warm airless places like Mercury or the lightside of Luna (although it would have to keep moving to stay in the light, and lunar eclipses would be greatly feared and traumatic). Or such a creature might appear on a rocky planet in a torch orbit.
Void-cold or void-fire creatures might show up on tidally-locked planets too if they are airless; it just depends on which side of the thermometer they prefer. There could be a hot and cold version of the same kind of void creature living on a tidally-locked planet, never really interacting because each side is too uncomfortable for the other variant.