>>8814691

Perhaps via a forgotten tributary of the Styx which leads via a dimensional gateway to Gensokyo. Incidentally, there's a Touhou-related version - a parody if you will - of Vanripper's creation:

https://www.youtube.com/watch?v=kZLw1jj-uEM

So I guess it's not impossible for a demon to visit that realm where Yokai exist.