A high fantasy setting where the PCs are coming from our world, from any historical period.
>They come with whatever they have at the moment, so a WWII soldier may arrive with his rifle, but will likely run out of ammo quickly.
>Isekai'd characters with little to no combat abilities (if you want to play a modern otaku, for example) can be paired with a character from the fantasy realm who can fight for them.
>They are not the only character from our world who crashed into this one, some of these may even be antagonists.
>Turns out this fantasy realm is a Super-Sargasso world of some sort, where beings and creatures from a wide variety of dimensions periodically pop up. Similarly, most of the monsters are castaways from other, weirder worlds.
I still think it's a fun idea, because it allows the players to crack modern jokes, try to pull all sorts of ploys and have fun interactions in-character, but fantasy isn't too much of my thing.