Also important: What is the relationship between the soul's fursona and an individual's patronus? Identical? Mostly independent? In a committed relationship? Druid and animal companion?
Mostly independent, of course.
The patronus is both a guardian to the wizard who casts it and a symbol of significance to their character, in the symbolic language of their culture and their inner life; that Harry Potter's patronus is a stag speaks to his relationship with his late father, for example. It says that James Potter is a symbol of emotional (if not physical) safety and protection to Harry, as a man who unconditionally loved Harry while he was alive.
The fursona, on the other hand, is more than just a symbol of personal significance to the person it belongs to; it is, in some sense, a symbol of the person it belongs to, a direct symbol of the self. The fursona is more than an extrinsic guardian to the person it belongs to; it is, in some sense, the intrinsic person himself. It is, if only superficially, everything that one hopes and wishes for, an earnest statement not of what the self "is", but of what the self "could be".
The fursona and the patronus are independant, but as they come from the same person, they can of course overlap. It's not a coincidence that when Harry sees himself casting the patronus charm for the first time, he sees his father: this shows us that Harry is comforted by the image of his late father, but also that Harry aspires to be like James, and takes some comfort in that. (And that's also why Harry feels doubly betrayed when he learns that his father wasn't perfect, etc.)
The current discussion is making me half-want to write an AU where Sabrina wished to be a furry and Firn had to figure out how to bullshit-potential that into being as rad-awesome as Griefbending.
See, what
could be more powerful than being a furry?
On a superficial level, to become your fursona is merely to assume "the shape that you wish you could inhabit" (the 'soulshape' or 'eigenself', perhaps, if we're lame and we wish to dispense of the terminology of anthropomorphism).
And make no mistake, even that power is supreme. It is the transubstantiation of an abstract idea into physical reality;
it is the outright Materialization of the Soul.
But on an esoteric level, what does it
really mean to become your fursona, to become your eigenself?
If the fursona is what the self "could be", without regard for "what is", then to be a furry is, if only in some measure, to embody that ultimate possibility which lies outside of conventional human existence. To become a furry is to escape "the self and the story which you have been given" and to become "the self and the story which you have made for yourself".
It is nothing less than a path towards the completion of the Great Work and the union with the Higher Self.