This book functioned in some ways as a Bildungsroman, a novel about the gradual, perhaps episodic, development of a young person, morally, spiritually, and psychologically. Quite often, this young person grows into society, accepting a role as an adult (or near adult), with its attendant responsibilities and opportunities.
Casiopea's development is not straightforward. Her development moves away from the social traditions of her small town. Does she develop toward the faster, more modern society she encounters on her journey? Or is there even something more different about her development? At the end of the novel she is riding around in a stolen car with a demon. That doesn't seem to be quite the same thing as having grown into the "modern" society she to which she has become exposed during her journey.
Hun-Kamé develops, too. While not a young person, taking on some of Casiopea's mortality changes him at each stage of the journey, and, at the end, he retains a tiny portion of his human heart, changing Xibalba in a small way, too. We don't know whether this change will last, but our story ends with that change.
What are your thoughts on this theme of moral, spiritual, and psychological development regarding both Casiopea and Hun-Kamé? Were their changes believable? Relatable (insofar as a god can be relatable)?