Morihiko Toriguchi, a news magazine editor, spearheads the investigation into a series of unusual crimes plaguing Musashino and Mitaka from August to October 1952. He works in close collaboration with crime fiction writer Tatsumi Sekiguchi and onmyōji Akihiko Chūzenji. Toriguchi travels by automobile with Sekiguchi and Atsuko Chūzenji to examine case-related discoveries, including severed limbs found within custom-fitted boxes placed in surrounding towns. His investigation involves obtaining and analyzing a list labeled "Onbako-sama," which details believers in a local cult led by self-proclaimed onmyōji Hyōei Terada. Toriguchi suspects Terada's involvement in the dismemberment case after observing that all identified victims were daughters of Terada's followers. During this analysis, he and Sekiguchi note two significant names on the list: Yoriko Kusumoto's mother and Gothic fiction writer Shunkō Kubo.

Later, Toriguchi participates in the confrontation at Kōshirō Mimasaka's research facility alongside Sekiguchi, Reijirō Enokizu, and other central figures, where the full scope of the crimes is uncovered. In the OVA special "Chuuzenji Atsuko no Jikenbo - Hako no Yurei no Koto," presenting Atsuko Chūzenji's investigative notes, Toriguchi appears in a car scene with Sekiguchi. Concrete information about Toriguchi's background, appearance, or character development remains undocumented in other official media such as films, manga adaptations, or spin-offs.