Takeshi Shinjō, a seasoned detective in the Tokyo Metropolitan Police Department’s Criminal Investigation Division, leads investigations into the "New Generation Madness Resurgence" serial killings. Partnering with colleagues Mio Kunosato and Katsuko Momose, he employs a methodical, analytical approach to cases, maintaining clinical detachment from their emotional stakes. Though outwardly stoic, he harbors a hidden sensitivity to graphic scenes, balancing professional rigor with quiet empathy for victims and allies alike.

His career was sparked by admiration for Yasuji Ban, a mentor figure whose unsolved murder propelled him into law enforcement. This pursuit of closure drives his involvement in the New Generation Madness cases, where he aids protagonist Takuru Miyashiro with strategic guidance and investigative resources. Interactions with associates like Hinae Arimura reveal a demeanor marked by cautious collaboration, as he prioritizes cold logic over personal ties.

Shinjō’s resolve stems from a past steeped in loss, his dedication to justice shaped by the need to honor Ban’s legacy and thwart future tragedies. His arc centers on navigating the grim realities of homicide investigations—dissecting moral ambiguities and gruesome evidence—while compartmentalizing the psychological toll. The narrative remains anchored in his role as a tenacious investigator, relentlessly unraveling the central mystery without deviation into undocumented expansions.