I loved David Levithan's novel Every Day about a teenage entity who wakes up each morning in a different body, but this prequel just didn't do it for me. I think the intent was to showcase how A adopted their principles and grew to be the kind of person who would fall for Rhiannon at the start of Every Day, but there's not really a huge disconnect between the characterization here and there, and I didn't feel like I learned anything new about A's character in this story. Read Every Day and consider the companion novel Another Day, but don't bother with this one.