Minoru Sagisaka is a detective in Shinjuku's Intervention Department, focused on investigating serial murders potentially linked to the supernatural. He works with his partner, Narumi Kure, mirroring the investigative dynamic of Mulder and Scully from *The X-Files* by pursuing cases others dismiss as ordinary crimes. Sagisaka's drive originates from personal tragedy: his daughter, Yoshiko, witnessed a mikura slaughter her classmates. Authorities declared her account delusional, leading to her commitment in a psychiatric hospital. This fuels his relentless pursuit to prove supernatural threats exist and validate his daughter's sanity.

Throughout the narrative, Sagisaka maintains a steadfast belief in the supernatural, countering his colleagues' skepticism. His investigations identify survivors of mikura attacks, including a young woman named Hinaru, as he collects evidence connecting the murders to these entities. During the climax, as chaos orchestrated by the antagonist Eko engulfs the city, Sagisaka, Yoshiko, Kure, and Hinaru seek refuge in an emergency shelter. Inside, the Chief of Police reveals himself as the mikura Ushi-oni—the very entity responsible for Yoshiko's trauma—and attacks the refugees. Recognizing the monster from his daughter's flashbacks, Sagisaka sacrifices himself by pushing Yoshiko clear during Ushi-oni's assault, resulting in his death. This action ensures Yoshiko and the others survive the encounter.

Sagisaka's character arc concludes with this selfless sacrifice, which directly enables Yoshiko's eventual recovery from her catatonic state. His efforts to expose the supernatural, though ended by his death, contribute to the broader resolution of the conflict in Shinjuku.