I found the easy resolution of various conflicts in this part
a little distracting. I kept thinking "how convenient" instead
of concentrating on Ranko.
On the other hand, I loved the treatment of Ranko learning the
violin.
And the resolution of the Genma situation was handled well;
after two chapters of leaving the reader hanging, Genma comes
across as simply stupid rather than malicious. Of course, you
gave us a broad hint of this in Part 2, with the brochure.
The bit about the chaotic nature of Happosai's spell was kind
of cute; I liked it. (However, like a few other matters, it's
not completely consistent with canon, and so does require a bit
of a leap of faith on your readers' part.)
My recommendation, for what it's worth, is that you leave in
a bit of schoolmate conflict, to be resolved in Part 4 if you
so choose, and just forget about Kodachi and the Principal
altogether. Have, say, one named girl and boy each as holdouts,
disliking the new Ranko, with small handfuls of unnamed
associates. No need, I'd think to dwell on them, just bring
them up so that the reader isn't thinking "TOO easy".