Imagine if Mokō (and if you believe the Fujiwara no Fuhito theory, Akyū as well) speaks in kansai dialect. Actually... the kansai one was the default dialect in the past. And given the nature of our cast, a lot more of them probably should speak in this dialect too. The prominence of the Tōkyō dialect is relatively recent.
And thinking about it, Gensōkyō definitely has characters from all across Japan who have migrated in. There are definitely all sorts of accents around beyond Futo and Mamizō. Nemuno comes to mind, who I'm pretty sure is speaking with the Tōhoku dialect. Reading out what she says in Japanese really reminds me of Megumi from Shokugeki.
By the way, Tōhoku is the top part of the main island.
