Assistant Police Inspector Shinobu Kujiin serves at the Tokyo District Public Prosecutors Office. He joins public prosecutor Zen Seizaki's investigation into a pharmaceutical company accused of promoting a defective drug and falsifying test results. This probe expands to encompass potential manipulation in Shiniki district's mayoral elections and efforts to legalize suicide.

As a key member of the investigative team, Kujiin readily crosses organizational lines to collaborate with colleagues such as Zen Seizaki and Atsuhiko Fumio. His demeanor is notably easy-going, yet he maintains professional competence and effectiveness in his police duties. He is recognized as a capable and reliable officer.