That title actually might be hitting on a few different things, because there are a ton of books that get nicknamed 'the kitsune book.' If you're talking about what I think is the most common one, people are usually referring to 'Kitsune-Tsuki' by Author, or sometimes the novel 'The Fox Woman' by Kij Johnson. I read 'The Fox Woman' years ago and it really stuck with me. It's a slow, atmospheric retelling of a Japanese folktale set in the Heian period, centered on a nobleman, his wife, and the fox spirit who becomes obsessed with him. The main plot isn't a fast-paced adventure; it's more about longing, transformation, and the painful gaps between the human and spirit worlds. The fox, Kitsune, yearns to become human to be with the man she loves, going through this intense, physical metamorphosis that's described in almost visceral detail.
I think what people remember most is the structure—it's told through alternating diaries from the man, his wife, and the fox. You get these three deeply subjective, sometimes unreliable, perspectives on the same events. The wife's sections are particularly haunting because she's the one slowly being displaced in her own home, sensing this otherworldly presence she can't quite pin down. The plot ultimately spirals into tragedy, as these things often do. It's less about a clear 'hero's journey' and more about the melancholy consequences of desire across a spiritual boundary. The ending left me feeling quiet and unsettled for days, which I guess is the point. I still flip back to the wife's final entries sometimes; they capture a specific kind of loneliness that’s hard to shake.