Nihonbashi is a Tokyo district that recurs as both a remembered destination and a marked-out landscape in the investigation. A recollection that Watabe went there, followed by a calendar listing bridges in the area, makes Nihonbashi a point of connection between personal history and an unexplained series of annotations.

A Place Recalled

Yasuyo recalls that Yuriko had mentioned a place with a grand-sounding name. The name comes back to her as Nihonbashi, prompting the detectives to confirm that she means the district in Tokyo. Yuriko had told Yasuyo that Watabe went there from time to time and liked to talk about its restaurants and famous sights.

The memory also contains a contrast: Yuriko said she had hardly ever gone to Nihonbashi when she lived in Tokyo. Yasuyo had never asked why Watabe visited, so the recollection supplies a detail but not its explanation. The district enters the investigation through what Yuriko chose to remember and what her friend did not think to ask.

The Bridge Calendar

Nihonbashi appears again through a calendar whose pages carry handwritten bridge names. The annotations cover every month: Yanagibashi Bridge in January, Asakusabashi Bridge in February, Saemonbashi Bridge in March, Tokiwabashi Bridge in April, Ichikokubashi Bridge in May, Nishigashibashi Bridge in June, Nihonbashi Bridge in July, Edobashi Bridge in August, Yoroibashi Bridge in September, Kayababashi Bridge in October, Minatobashi Bridge in November, and Toyomibashi Bridge in December.

The investigators identify all twelve as bridges in the Nihonbashi area. Searchers had considered whether they marked events attended by Koshikawa, but their inquiries found nothing to support that possibility. The calendar is returned to its box without an interpretation, leaving the bridge sequence as a pattern whose apparent order is clear but whose purpose is not.

Investigative Context and Significance

Nihonbashi is also where Kaga is stationed: formerly in the TMPD Homicide Division, he now works in the detective bureau of the Nihonbashi Precinct. He and Matsumiya are cousins who had worked together on an investigation several years earlier; when they meet over beer and boiled broad beans, Matsumiya has something he wants to discuss with him. The district therefore belongs not only to the clues but also to the detectives’ working geography.

Across these references, Nihonbashi gathers disparate traces without resolving them. It is a place Watabe visited and Yuriko rarely did, a district mapped by a dozen bridge names on Koshikawa’s calendar, and the setting of Kaga’s current assignment. The gap between those concrete associations and the unanswered question of what they mean keeps the location active as an investigative lead rather than a solved explanation.