Masashi Nishiki is a detective serving in the Metropolitan Police Department's First Investigative Division. He is introduced as a minor antagonist whose role later shifts to that of an ally. For six months prior to the events of the story, Nishiki has been searching for his younger brother, Yuu, who vanished without a trace. This personal loss drives his professional focus, leading him to investigate a series of mysterious disappearances involving children and young students. He and his partner, Shigenobu Murakami, are assigned to look into these cases, which are sometimes called spirited away incidents. Nishiki is characterized as a diligent and serious officer who approaches his work with earnest dedication. His primary motivation is the hope of uncovering information about his missing brother and stopping further disappearances. In the unfolding narrative, he becomes entangled with the illusionary school created by the Executive Magatia, an antagonist from the monster army. Through this encounter, his path crosses with the central conflict between the Dragon Keepers and the monster forces. His relationships include a professional partnership with Murakami and his deep personal bond with his brother. Over the course of the series, Nishiki develops from being an obstruction to the main protagonist's goals into a cooperative figure. His notable abilities are those of a trained police detective, including investigative techniques and standard law enforcement skills; he does not possess any supernatural powers.