I hope Mayu shows up as well, and I have some confidence in that.

And I agree on Shunpei becoming Wajima's apprentice was definitely something that should have at least been built up to earlier; I felt Wajima's "wait, when did you want to do this?" was kind of a lampshade hanging over the lack of buildup for that plot point. As I mentioned in the review, there was a dire lack of buildup on a lot of stuff, this included.