In Shinto, when the shrine maiden dances the Kagura, it's said she becomes the Deity.
When Soh is summoned as a messenger of the Deity, is it Yoshiro who is the Deity in that moment?
Masks are also a channeling device. In the ending, Yoshiro is holding a mask as Soh leaves.
But the mask fades away from Soh's face, she doesn't grab it. Is it meant to reveal she was holding it herself the whole time and using it? Is that why the scroll of Soh fighting is called Kunitsukami? Because she's dancing the Kagura, becoming divine?
I suspect Soh is her soul, who wore the mask.
Extra:
She looked pretty here...