The skeletons don’t refer their universe as things such as Undertale, Swap, Fell, or anything like that. They use the code that each universe has been assigned with; AU01, AU02, AU03, AU04, AU05, AU06.
The current headcanon is that Frisk/Chara haven’t fallen down into the underground yet or never will. At the very least not in AU06. I don’t have any plan for the humans in this story.
This is a fontcest and papcest fanfic. There will be NSFW/sexual situations.