Inspector Junichirō Sakaki works at police headquarters. His initial encounter with Rem Ayanokōji occurred during a demon nightmare incident involving his daughter Yukari. Conflicting accounts exist: one depicts Yukari surviving due to Rem’s intervention, while another describes her perishing during the event. Though officially commended for meritorious service afterward, he harbors enduring self-doubt about his capability to confront bizarre or supernatural threats. This perceived inadequacy drives him to consistently seek Rem’s expertise on cases involving paranormal phenomena or dream disturbances.

He functions as a recurring contact for Rem’s detective agency, regularly supplying case details, official data, or logistical support for police investigations into mysterious deaths and disappearances tied to dream demons. His position establishes him as a liaison between conventional law enforcement and Rem’s specialized supernatural inquiries. During field operations, he occasionally participates in combat against manifested entities but proves markedly less effective than Rem or her allies.

His background includes no significant family besides his daughter. Across the original OVAs and "New Dream Hunter Rem" series, his character development remains centered on his role as a dedicated yet frequently overwhelmed inspector contending with incomprehensible forces. The trauma from his daughter’s ordeal fundamentally fuels his reliance on Rem and his engagement in subsequent supernatural cases. No substantial expansion of his backstory or significant evolution in his character arc occurs beyond this established pattern of involvement.