This series revels in contradictions and that is why I love it. The Summer of the Ubume delves into much of the basic logic Kyogokudo uses in his "onmyoudou practice" and "exorcisms", which are basically methods to snap a person awake from their delusions using a bit of sophistry rooted in Japanese folklore. He is more of a psychiatrist than a magician despite appearances to the contrary. In a lot of cases the author himself is a very similar person, a folklorist who doesn't actually believe in ghosts or religion, and strive to find rational explanations for myths and legends which in Japan's case often gradually evolved from rumors or embellished stories surrounding actual events. But at the same time he doesn't fully reject the concept of the supernatural: for him, the supernatural is merely a phenomenon which we haven't fully and rationally understood. This position is the exact same held by Kyogokudo the character - not surprising coming from an author who apparently cosplays as his own character 24/7 lol.
People questioned why he just accepts Reijiro's ability - it was explained quite lengthily by Kyogokudo in a previous book that Reijiro is basically a mutant who can detect and interpret subatomic particles that are traces of other people's (and IIRC even objects') memories. Not to the epic extent of the X-Men obviously, but once we accept that such a mutation is probable, no matter how small the probability is, then it makes perfect logical sense if a bit too convenient for the plotting. This explanation also came after Kyogokudo discussed the meaning of being alive and/or sentient with Sekiguchi where Kyogokudo made a point to explain his perspective on memories, obviously so he can lead the reader into accepting that yes, it is probable for Reijiro to have such a mutation.