Hmm. Was wondering what Kaori was, so I tried to find a yokai that fits her - best I could come up with (some brief Googleing some of her traits) and I think maybe a Ningyo - almost like a mermaid, but one of the folktales has a fisherman catching a Ningyo (which looked like a fish with a woman's face I guess?) that eventually grows up to become a beautiful young woman whom never ages beyond looking 20. The Ningyo in the story was going to be cooked by the fisherman, but a guest noticed the human face and saved her - eventually she outlivea her old husband. Maybe that kind of ties to Kaoris beauty, youthfulness, affinity to the kitchen, and her old husband we see towards the end here.
All that said, this is kind of a cobbled together theory, could be hella wrong, as what I know about yokai and Japanese mythology in general comes from manga, anime and LNs plus a bit of Google here and there. Anyone else have a guess?