You die - maybe? Or did you just fall down a hole? Really, it doesn't matter how it happened, the point is you got isekai'd, or transported to a different world.

You open your eyes to see the new land before you. How strange - this isn't a starter town or anything...

A few more moments of exploring and between the ominous geography and various monstrous entities, you're pretty sure you're in a demon realm.

Well, what do you do now?