When Soh purges defilement from herself/the former Yoshiro, it is Yoshiro who ascends to being a goddess. I'm now certain I was right. Soh is Yoshiro's soul.
Reminds me of the Double in Castenada, and the idea of the soul as the eternal friend who is both an other and you.
The soul also leads the mind and body, much like how Soh guides and leads Yoshiro through the spirit path.
