This one's got a slow start and it takes a while for the recurring cast to get dragged into the case, but it's a fascinating story that manages to tie together old myths, religious references, and history (all of which the scanlator has done a great job of informing us in the chapter notes) into the interlocking struggles and stories of several people. More than Box of Goblins, this really feels like something that could have happened in its place and time, and it's a much more 'fair' mystery than Summer of the Ubume, since the whodunnit is served up on a platter, and the whydunnit is the interesting part.
Look, any time the detective exorcist starts his 'revealing the mystery' speech with "Freud's theories are GARBAGE!", you know it's gonna be good.
This is the best Kyougoku Natsuhiko novel with a scanlated manga.