Nihonbashi Precinct is the local police district where Kyoichiro Kaga serves after transferring from the Tokyo Metropolitan Police Department Homicide Division. It is both his professional home and the institutional bridge that brings him back into an investigation whose clues intersect with his private history. The district’s everyday work, its local geography, and its formal cooperation with the homicide task force all become part of the novel’s account of how a case is reconstructed.

Identity and Setting

Kaga is assigned to the detective bureau of Nihonbashi Precinct. He had previously worked in the Tokyo Metropolitan Police Department Homicide Division, and he and his cousin Shuhei Matsumiya had investigated a case together several years earlier. Their professional paths now run through different parts of the police organization: Matsumiya is working on the current murder investigation, while Kaga is serving at the local precinct.

The transfer places Kaga in a setting where local responsibilities are concrete and varied. Soon after arriving, he is asked by the station commander to help teach at a children’s kendo workshop organized by the Nihonbashi Police Department. Because Kaga has a sporting background and is new to the station, declining the request is not a realistic option; he dutifully goes to the Chuo City Sports Center in Hamacho Park, where the workshop takes place in a basement dojo. The episode gives the precinct a community-facing role beyond criminal investigation, and establishes Kaga’s local service before the murder case draws him into wider police work.

Kaga’s Local Work and the Case

The kendo workshop also connects the precinct to Hiromi Kadokura, a theater director responsible for three child actors who need intensive kendo preparation for a play. Kaga recalls that he suggested finding child performers who already knew the sport, but Kadokura explained that the children also needed to act well and look right for their roles. The encounter gives the detectives a firsthand point of contact with Kadokura, whose birth name is Hiromi Asai, and ties Kaga’s new posting to a person central to the investigation.

When Matsumiya later shares details of the murder investigation with Kaga, he does so despite his usual reluctance to discuss an active case with outsiders. Their family relationship and previous experience working together make Kaga an exception. In a fast-food restaurant near Ningyocho Boulevard, Matsumiya describes the woman found murdered in the Kosuge apartment and the evidence gathered so far. Kaga focuses on the victim’s movements: the absence of signs in the autopsy report that she had been knocked out or restrained makes it more likely she went to the area voluntarily. He then tests the circumstances against the possibility that she went there on her own before intending to return home.

Kaga considers, but does not accept, a more elaborate scenario in which the victim was killed elsewhere and her body transported later. Hiromi Asai owns a Toyota Prius, and it was at the theater on opening day; she had also been busy there, which might have offered a chance to leave without attracting notice. But Kaga cannot make himself regard the hypothetical opportunity as convincing. His reasoning illustrates a distinction important to the investigation: a possible route and a vehicle do not, by themselves, establish that an action occurred.

From Precinct Cooperation to the Task Force

Kaga’s work at Nihonbashi does not keep him outside the larger investigation. He offers Matsumiya a way to rethink the case by asking what sort of life the otherwise elusive Mutsuo Koshikawa had been living. The suggestion turns attention away from the mere absence of records and toward the possibility that reconstructing a hidden life could explain the case. At the same time, Kaga continues to have the obligations of his local post; he leaves a discussion to return to Nihonbashi, where he says he has a great deal to do.

The decisive institutional link comes when Kaga tells senior investigators that his mother had a long-term relationship with Shunichi Watabe. He has found a handwritten list among her belongings whose twelve bridge names and month-by-month arrangement match the information on Koshikawa’s calendar. Kaga cannot establish who wrote the note or what it means, and asks the task force to arrange handwriting analysis. He also offers to turn over his mother’s possessions if they may assist the inquiry. The information gives the investigators a reason to examine a family connection without treating Kaga’s own guess about the writer as proof.

After consultation with the Homicide Division section chief and the commissioner, the task force makes an official request for assistance from Nihonbashi Police. Kaga is then formally assigned to the investigation team. The move changes his position from a local detective advising his cousin to a member of the joint inquiry, with the precinct’s cooperation providing the proper institutional route for his participation.

The Precinct’s Reach and Narrative Role

Nihonbashi’s importance is also geographical. The case’s investigation follows the victim’s movements and asks whether a suspect could have reached a car, left a theater unnoticed, or transported someone to Kosuge. Later, Kaga’s reasoning draws on the significance of the Meijiza Theater in the district: it was where Hiromi Asai first performed, and he believes it held meaning for both her and her father. He proposes that Tadao Asai may have attended the opening night, and that Michiko Oshitani, who bought a same-day ticket, may have seen him there. These are presented as deductions to be tested, not as facts that the precinct itself can establish.

The district therefore functions as more than a police boundary. It brings together the theater, the bridges that surface as clues, and Kaga’s local knowledge, while the formal request for assistance connects the precinct to the metropolitan investigation. That combination mirrors the case’s wider method: a clue becomes useful when its location, relationships, and evidentiary limits are considered together. Kaga’s transfer to Nihonbashi had placed him near the setting; the investigation turns that proximity into a route back into the case.