I think an Earth C entry in the Friendsim series could totally work, though I think a visual novel is exactly the wrong medium through which to explore the establishment of the Four Kingdoms, even in the name of more exile content. Those guys deserve a story of their own!

C-quest (C-change? C-side? WORKSHOP TITLES HERE FOLKS) would work best focusing on a cast of everyday Earth C schmoes the same way Friendsim does, imo, and most of them should be living around the same time in the interests of fully fleshing out a particular slice of the world they live in. A handful of trolls, a handful of humans, some Furthest Ring ghosts (I immediately presumed we were doing the Candy volume as a setting, but I guess that would be a whole other thing that needs discussing), so on for carapacians and consorts... I always forget the consorts can talk. Hell they're probably chattier than most chess folk are. I'm just dying to know what a four foot crocodile has to say about the rise of Neo-American fascism