I will say up front that I did not read the fluff content. I bought it entirely for the mechanical options. Feats, items, archetypes, etc. The biggest downside of this content is that it make so much of the core rules ancestry content feel half baked. A lot of the ancestries in the core rules feel like they were written by someone who was told to design rules for the ancestry and did an hour of google for some basic inspiration for the theme. This supplement feels like it was written by someone who personally loves the idea of the kitsune and wants to see it pop when someone plays it. I think it might actually manage to cause some complaints at the table, not because it's overpowered, but because the player will actually be drawing attention to their ancestry more than everyone else does. Because their ancestry will actually be relevant and interesting and not just some faint background scent like a can of La Croix.
Ancestry Guide Kitsune: "I'm a furry."
Kitsune of Golarion Kitsune: "I'm a cunning shapeshifting trickster from a mystical lineage with deep rooted customs and traditions. I'm also furry. Or am I? Hmmm, isn't that curious..."
[5 of 5 Stars!]