Ryuichi Murakami works as a corporate employee at the same company where protagonist Hoichiro Oma maintains his daytime identity. His position enables routine interaction with colleagues, including Oma and accounting staff member Keiko Yamamoto. Murakami commits significant financial misconduct alongside his superior, Koji Kawamata, specifically embezzling company funds. To facilitate the embezzlement, Murakami exploits a personal relationship with Yamamoto, manipulating her through seduction and false promises of a future together. This manipulation coerces Yamamoto into granting illegal access to the financial systems or records required for the theft.

When an internal investigation into the missing funds commences, Murakami pressures Yamamoto to vanish, taking the stolen money to divert suspicion from himself and Kawamata, intending her to be the scapegoat. After Yamamoto complies, Murakami takes drastic action to sever ties to the crime. He is directly implicated in her subsequent death, implied by his reactions and a private monologue to be a staged suicide. The official police investigation rules her death self-inflicted, a finding Murakami accepts without challenge.

His criminal actions attract the attention of the supernatural entity known as the Judge of Darkness. This entity, secretly Oma acting under underworld authority, targets Murakami for escaping earthly consequences. The Judge confronts Murakami directly, formally charging him with Yamamoto's murder and detailing his embezzlement using a supernatural ledger. Murakami attempts to evade judgment, displaying fear and desperation, but his efforts fail against the Judge's powers. A demonic entity manifests, physically assaults Murakami, and causes a fatal fall, ensuring his supernatural execution.

His character arc is confined solely to the events depicted in the original video animation. His role serves primarily to initiate the core conflict involving the Judge and Kawamata, concluding definitively with his supernatural execution.