I'd love to hear more about the people that are unassociated. Are there people who lack a domain's affiliation altogether? How are they treated by deities and those that serve them? Is such a thing common, or a truly rare occurrence?
These people are actually the most common. While being a citizen of a nation makes you obligated to uphold its domain, it doesn’t mean you’re linked to the domain on a deeper level.
Aspects of a nation, those who are actually linked to the domain, are usually higher-tier members of the military, nobles, members of the government who are specifically in charge of keeping the domain of the area in check, and researchers (Typically Alchemists).
The average citizen isn’t as in-tune with the idea of domains either, but does believe that their protectors are powered by this mysterious astrology. They get to see these miracles called songs up close often enough. Some really get into the belief in their nation’s domain as a source of faith, some are less interested and just try to live out their lives knowing their country protects them.