"Mōryō no Hako" is a 12-episode anime series based on the mystery novel by Natsuhiko Kyogoku. Set in 1950s Japan, the story intertwines supernatural folklore with psychological and criminal investigations. The narrative revolves around a series of gruesome murders involving dismembered bodies found in boxes, which draw the attention of various characters connected through their expertise in folklore, psychology, and detective work.

The central figure is Akihiko Chuzenji, a folklore scholar and exorcist known as "Kyogokudo," who investigates supernatural phenomena. He is joined by his assistant, Sekiguchi, a young man with a keen interest in the occult. The pair become involved in the case after encountering Kureha, a high school girl who claims to have witnessed a ghostly figure connected to the murders. Kureha’s mental state becomes a focal point as her experiences blur the line between reality and delusion, raising questions about her reliability as a witness.

The investigation expands to include Toriguchi, a detective determined to solve the case through conventional means, and Enokizu, a reclusive psychic with the ability to perceive the memories of objects. As the characters delve deeper, they uncover a web of interconnected events tied to a mysterious box said to contain a "mōryō," a malevolent spirit from Japanese folklore. The box becomes a symbol of both the physical and psychological horrors faced by the characters, as they grapple with the possibility that the murders may be linked to supernatural forces or the darker aspects of human nature.

The series explores themes of perception, reality, and the intersection of folklore and modernity. The narrative structure is non-linear, with frequent shifts in perspective and time, reflecting the fragmented nature of the investigation. The characters’ personal histories and psychological struggles are gradually revealed, adding depth to their motivations and interactions. The resolution of the story ties together the supernatural and psychological elements, offering a complex and thought-provoking conclusion to the mystery.