I would probably go the route of: The people who first set up a colony on Neptune. Maybe some of them went off on missions to other parts of the galaxy. Then got separated from Neptune. Then when Neptune became hidden from our Vanguard it also became lost from that other group too. Maybe they ran across darkness powers first. They could have Stasis, Strand and a third dark subclass. Since they started with darkness, maybe each would be more developed and each have 2-3 supers. They start finding clues or hear rumors that a military force of humanoids survive on a distant planet but forces on some kind of “odd or even dangerous “ light powers. When they hear of this, they start sending spies into the Vanguard ranks to see if we can be trusted or if we should be their enemies. They have taken more of a CIA/ spy agency approach vs the Vanguards more military forward approach.