There is no reason to believe there is such a thing as a soul, most frequently the term is left undefined because that is where the power of the imagination is free to range in the land of the undefined.
I believe there is a commonality in life forms, essentially the same thing manifest into different forms. The soul being undefined, this commonality of life might be termed soul. Example, "The Self In One Is The Self In All," Upanishads.
You have chosen a rather tuff or perhaps easy subject, for no matter what you say about the soul, your guess is as good as any. So he says as he rides away on his unicorn. Personal identity is a challengeing topic as well but not of necessity being the soul, though it would be a more reasonable premise than the elusive immortal soul.
What is a myth? The dictionary definition of a myth would be stories about gods .... What is a god? A god is a personification of a motivating power or value system that functions in human life and in the universe -- the powers of your own body and of nature. The myths are metaphorical of spiritual potentiality in the human being, and the same powers that animate our life animate the life of the world ...
"We need myths that will identify the individual not with his local group but with his planet." Joseph Campbell