Detective who works under Detective Gotou and who starts out loving the supernatural but after experiencing it first hand is scared of the supernatural. However, he still remains very interested in supernatural phenomena, at times suggesting the causes behind events are because of it.

Although Gotou doesn't think too highly of Ishii, Miyawaka and Yakumo thinks highly of Ishii. Throughout the series, Ishii slowly changes into a person more sure and confident of his abilities, even later starting to voice his opinions against Gotou. He admires and respects Gotou, wanting to be a detective like Gotou. He has a crush on Haruka.