I put it on the list, but there is actually an Overtale that's been running for a while now. Different plot, but I do suggest you check it out in case it has some of your interests in it.

That's why I'd rather go Losttale or Othertale.

Now for Othertale...I was thinking of having it with different sealing conditions, it set in one of these possible places:
-Under a major city
-A lost island
-Underwater
-Under a reservoir
-___ underground location