Nihonbashi Bridge is more than a landmark in the district that bears its name: it is one of the places through which the novel’s private family history becomes legible to investigators. A handwritten list and a calendar independently identify it as the July bridge in a sequence of twelve. Later, the annual bridge-washing ceremony places Hiromi Asai in a photograph that helps Kaga uncover her connection to Shunichi Watabe—and the truth that Watabe is her father, Tadao Asai.

Setting and Place in the Bridge Sequence

Nihonbashi Bridge appears as the seventh stop in a twelve-month list of bridges in the Nihonbashi area. The sequence begins with Yanagibashi Bridge in January and moves through Asakusabashi Bridge, Saemonbashi Bridge, Tokiwabashi Bridge, Ichikokubashi Bridge, and Nishigashibashi Bridge before reaching Nihonbashi Bridge in July. It continues with Edobashi Bridge, Yoroibashi Bridge, Kayababashi Bridge, Minatobashi Bridge, and Toyomibashi Bridge through December. The same annotations appear on Mutsuo Koshikawa’s calendar and on a note found among Kaga’s mother’s effects. Their exact correspondence turns an otherwise puzzling list into a shared clue, though its meaning is not immediately apparent to the investigators.

The bridge’s July placement initially prompts a search for a connection to seasonal events. Matsumiya considers whether the Tanabata Star Festival or the Tanabata Yukata Festival might explain the choice, but learns that the yukata festival has no direct connection to Nihonbashi Bridge. The more relevant July event is Hashiarai, the annual washing of the bridge. The distinction matters: the clue is not simply a bridge paired with a month, but a bridge associated with a particular recurring occasion.

The Bridge-Washing Ceremony

During a boat journey through the bridges, Matsumiya and Kaga reach Nihonbashi Bridge after Nishigashibashi Bridge. Matsumiya looks up at its iron lampposts and kirin statues, a stately landmark amid the route’s succession of bridges. The boat then continues past Edobashi Bridge, Yoroibashi Bridge, Kayababashi Bridge, Minatobashi Bridge, and Toyomibashi Bridge before returning by way of the Kanda River. The journey makes the list’s geography concrete while the detectives consider what its order might encode.

Kaga later tells colleagues that he has gathered photographs of the annual washing of Nihonbashi Bridge. His collection numbers just under five thousand images, assembled from a wide range of sources. In one photograph, children scrub the road surface with brushes while adults watch and take pictures. That activity occupies the background; the photographer’s chosen subject is a woman in the foreground: Hiromi Asai. Terumasa Yaguchi, who took the photograph, says that she happened to be there and that the occasion seemed otherwise ordinary. The image’s importance lies not in a special public event, but in the person inadvertently recorded within it.

A Private Meeting in a Public Place

The bridge sequence began as a practical solution to the problem of keeping father and daughter in contact without attracting attention. Hiromi and Tadao could speak by mobile phone while standing on opposite sides of a river or canal, close enough to see one another’s faces but not obviously meeting. Because returning to the same bridge every month risked notice, they chose twelve different bridges in the Nihonbashi district. The district carried particular meaning for Hiromi because it was home to the Meijiza Theater, where she had first performed.

Hiromi bought two mobile phones and mailed one to Tadao. Their next meeting took place at opposite ends of Edobashi Bridge, the designated bridge for August. In July, Nihonbashi Bridge served the same purpose. The monthly entries therefore record a private pattern concealed in an apparently public, geographical list: a way for a father and daughter to speak face to face while maintaining distance. The bridges do not merely mark where they met; their rotation was part of how they tried to avoid being recognized.

The Photograph and the Uncovered Truth

The bridge-washing photograph captures Hiromi at the point when the private arrangement became vulnerable to chance. Her birthday was approaching, and Tadao had complained that he had not seen her face for too long, so they arranged to meet in July at Nihonbashi Bridge. Neither knew that the washing ceremony would take place that day. When Hiromi arrived, the bridge was crowded, but she quickly spotted Tadao at the far end. She removed her sunglasses so he could see her face. She did not know that someone would photograph her at that moment.

Years later, Kaga’s attention to this image gives the unplanned sighting investigative force. Hiromi recognizes that he confronted her with the photograph and assembled small mistakes and circumstantial details into an account of the truth. The image itself does not disclose everything: it records Hiromi, while the surrounding investigation connects her to Watabe and establishes that Watabe was in fact Tadao Asai. Nihonbashi Bridge is thus where a concealed relationship leaves a visible trace. The bridge-washing ceremony, ordinarily a recurring public event, becomes the accidental record through which a private family history can be reconstructed.