Brown acts as the steadfast assistant to the titular detective, consistently accompanying them during investigations and case-solving. In "Eiga Oshiri Tantei: Sufūre-to no Himitsu", Brown travels with the detective to a new city to sample the special "Sufūre-to" cake. After the cake is stolen, Brown joins the investigation into its disappearance and related mysterious incidents plaguing the city. Throughout this case, Brown interacts with key figures like Cream the baker and the enigmatic cat Mocha, gathering vital clues. Brown's involvement includes collaborating with others to decipher puzzles and confront a secret organization behind the events.

Across the broader franchise, Brown reprises the assistant role in multiple theatrical releases: "Eiga Oshiri Tantei Shiriarty", "Eiga Oshiri Tantei Curry Naru Jiken", "Eiga Oshiri Tantei Tentō Mushi Iseki no Nazo", "Eiga Oshiri Tantei Star and Moon", "Eiga Oshiri Tantei Saraba Itoshiki Aibō (Oshiri) yo", and "Eiga Oshiri Tantei Yume no Jumbo Sweet Potato Matsuri". Brown also appears in the television special "Oshiri Tantei Cosmic Front", assisting the detective in solving cases that incorporate educational elements about dinosaur research and space rockets.

Brown's primary narrative function centers on supporting the detective during investigative activities across all confirmed appearances. No concrete information exists regarding Brown's personal background, physical characteristics, or independent development outside this assistant role.