Tsukimaru Nishimura served as a field agent for the Kura organization, specializing in collecting cognition particles at crime scenes using the Wakumusubi device to aid serial killer investigations. He collaborated with the metropolitan police on homicide cases and suspect apprehensions.

A tall young man with short brown hair and grey eyes, Nishimura typically wore a black suit, white shirt, and cyan tie. His demeanor was generally amicable and approachable, though his casual attitude could occasionally be perceived as smug or condescending by those outside Kura, unintentionally so; he maintained a good-natured attitude and expressed professional respect for colleagues, demonstrating focus and efficiency during investigations.

His specific case involvements included confirming the identity of Yuji Oonuki at his parents' residence during the "Jigsawed" case and relaying information to the Wellside team, investigating the Pyrotechnician's crime scene in "Sniped" to collect cognition particles, and detecting unexpected particles during the "Extended" investigation into the Gravedigger's kidnapping of Keiko Kikuchi, where he acknowledged forensic team skepticism while maintaining professionalism.

Nishimura's final operation occurred at the Kazuta family estate during "Fallen." Searching for victims with SAT teams, he noted wires on soy barrels and suspected concealed victims. As SAT opened one barrel, he continued scanning for cognition particles. The barrels contained gasoline instead of soy sauce, triggering an explosion that killed him and most personnel present. His funeral was held several days later in "Circled," attended by Kura and Wellside members.

His name combines "tsuki" (moon), "maru" (round/purity), "nishi" (west), and "mura" (village).