Arcana is a story that weaves humor throughout and primarily follows two detectives, Murakami and Nakabayashi, as they work with a mysterious girl who possesses the ability to see spirits. The plot centers on a case involving serial bombings that specifically target elementary school children, leaving the detectives stumped and without leads. Their only hope is a patient with amnesia from a nearby mental clinic, who may be able to provide them with a prophecy that will guide them to the truth. The plot thickens as supernatural occurrences become more frequent, and the detectives must also uncover the enigmatic girl's secret. To further complicate matters, they are reassigned to new jobs.
