Ishinomaki is a key location in the investigation because forensic fingerprints link Mutsuo Koshikawa to its station and suggest that he traveled there from Sendai. The route offers a concrete lead, but not an explanation: investigators can establish that he went to Ishinomaki, while the reason for his visits remains a question.

Setting and Investigative Clue

The relevant evidence comes from a page in a paperback timetable giving the departure times for the Sendai Line, which runs from Sendai to Ishinomaki. The page was so dark that its text could not be read normally; forensic examination using special lighting and a filter revealed green-tinted fingerprints along its edges. Further tests found a particularly high concentration of prints at Ishinomaki Station.

The concentration made Ishinomaki more than a place named in a timetable. It tied Koshikawa to a particular station and supported the conclusion that he had traveled between Sendai and Ishinomaki. The detectives could not determine how often he made the journey, so the evidence established movement without establishing a routine.

What the Route Does—and Does Not—Reveal

When Matsumiya asked whether Koshikawa had often traveled between the two cities, Kobayashi drew a careful distinction: he could not speak to the frequency, but Koshikawa had gone from one place to the other. The limit matters. The fingerprint finding narrows the inquiry to a real connection with Ishinomaki, yet leaves the purpose of the travel unresolved.

The suggestion that Ishinomaki’s fishing industry might explain the journeys is posed as a possibility, not confirmed as the answer. The location therefore functions as an investigative opening: a physical trace gives the detectives a direction to pursue, while the reason for the trip remains unknown.

Place in the Wider Investigation

Ishinomaki also belongs to the investigation’s broader effort to reconstruct relationships from incomplete records. Elsewhere, a profile identifies Hiromi Kadokura as having been born Hiromi Asai in Shiga Prefecture, while Kaga tells his superiors that his mother had a long-term relationship with Shunichi Watabe. Later, Kaga argues that Watabe’s long connection with Hiromi Asai, his limited ties to others, his estimated age, his disappearance, and his acquaintance with Michiko Oshitani point to Watabe being Hiromi’s father, Tadao Asai.

These findings do not establish that Ishinomaki was connected to Watabe or to the Asai family. Rather, the novel places the travel clue alongside a separate reconstruction of identities and ties: in both strands, investigators assemble a larger history from fragments whose meaning is not immediately apparent. Ishinomaki’s particular contribution is narrower and concrete—the evidence places Koshikawa at its station, but does not yet explain why he went there.