Ok so this might be too obscure for anyone to find, I think it was possibly 1-2 chapters at the end after the main story(that I can't remember). A boy goes to visit a shrine, there's a fox statue at the entrance. When he goes there again the statue is gone and a boy is there, he thinks that he's the spirit of the fox statue (turns out the statue was just away being repaired or cleaned) might be misremembering the details...I've been searching forever but I can't find it
So I guess it's AI anyway but like this is still so weird, why make it look like that... I've read the novel and his animal form is just a normal squirrel (well, technically a siberian chipmunk I think). He's supposed to be an adult that can turn into an adult animal.