Junichirō Sakaki works as an inspector for the metropolitan police headquarters. His first meeting with the protagonist stemmed from a supernatural investigation concerning his daughter, Yukari, who suffered from demon-induced nightmares. This case forged both their professional association and personal connection.

Despite official commendation for resolving his daughter's case, Sakaki developed enduring feelings of professional incompetence. These self-perceptions arose from repeated exposure to bizarre phenomena outside conventional police work, solidifying his reliance on specialized assistance for supernatural investigations.

In cases involving dream demons and paranormal occurrences, Sakaki primarily acts as an information resource and official liaison. He supplies case details and accesses law enforcement resources to support operations against supernatural threats. Though lacking metaphysical abilities or specialization in dream combat, he occasionally engages in real-world confrontations when feasible.

Sakaki exhibits recognizable physical traits, including facial hair and a habitual smoking habit, consistent across series media. Professionally, he maintains a pragmatic approach to police work while demonstrating adaptability when facing supernatural elements.

His relationship with the protagonist extends beyond professional boundaries, evolving into a protective, quasi-paternal dynamic. This is particularly evident during cases involving young victims, where his personal history with his daughter's ordeal informs his deep investment in achieving resolutions.

No substantial character development or expanded background is documented in sequel OVAs ("New Dream Hunter Rem"), spin-off manga ("Dream Hunter Rem XX", "Dream Hunter Rem Alternative"), or video game appearances ("Super Heroine Chronicle"). His role remains consistently that of a supporting law enforcement contact throughout all confirmed appearances.