cursed isekai concept, body horror
When transported to another world, the magic takes all of "you" to that world. The magic only classifies your brain and nervous system as "you", leaving your brainless/nerveless body behind.
Perhaps the magic ritual follows up with growing you a new body, but good luck getting back to your original world. It may require some form of magic on the Earth side as well to reverse the process, given your original body is likely to up and fail shortly after your leave.
