Hidenobu Osanai is a colleague of Shizuma Origasa in the newly formed Imperial police force. He assists in operations against Edo's criminal elements, notably conducting an unauthorized investigation into Zenbei Kuraya's activities. Osanai and Shizuma confront Kuraya upon discovering his leadership of a "hunting club" that murders women at night, an operation driven by their exposure of Kuraya's predatory pastime. Together, they intervene to rescue Koume during her pursuit by Kuraya's group. Police reinforcements later aid in capturing Kuraya and his associates. Osanai's story concludes with his death in the series, as documented among characters who meet their demise.