Godheart

TLDR: A supernatural entity of your choice has taken residence in your head and you've been isekai'd to a world of your choice. (with LL's Inner Life) You are a normal person living on Earth when you are suddenly inhabited by a god/demon/fey/other who is on the run. Their pursuers drag them back to their own world, and you along with them. You manage to get flung off course and land somewhere far from your intended destination. You are now in a fantasy world with a tenant living in your head.