Kyo Kaga–Shuhei Matsumiya cousin relationship

The cousin relationship between Kyoichiro Kaga and Shuhei Matsumiya is both a family bond and a working partnership: Matsumiya participates in investigations that touch Kaga’s private history, and their exchanges turn inherited family experience into a guide for detective work. Their closeness is visible not only in what they know about one another, but in the way they can recognize the personal meaning beneath an apparently ordinary investigative choice.

Family History and Shared Loss

The cousins’ family history includes the death of their uncle, Takamasa Kaga, and the unresolved question of Kaga’s mother, Yuriko. Kaga explains that his father believed Yuriko had done nothing wrong and was convinced that, before she died, she must have wanted to see her son, even briefly. The thought caused Takamasa great pain. His restraint was part of that grief: he apparently believed that pursuing Yuriko would not help either of them, and blamed himself for failing to help her through her mental health difficulties.

Matsumiya connects this history to another family decision. He recalls that Kaga and Takamasa had agreed Kaga would not visit his uncle even when Takamasa was critically ill; Takamasa had decided he wanted to die alone, and Kaga was absent when he died. The recollection makes the cousins’ shared family past more than background: it is a history of painful separation, decisions made out of consideration for another person, and loss that cannot be undone by later understanding.

A Working Partnership

The relationship also takes shape through their investigative collaboration. When Matsumiya tells Kaga about the suspicion that Hiromi Asai had a former lover she could not forget, Kaga tests how that possibility fits the case and asks whether the task force still regards her as a suspect. Their conversation shows Matsumiya bringing information to Kaga and Kaga weighing it against the investigation, rather than treating their kinship as grounds to abandon professional judgment.

That distinction becomes explicit when Kaga reflects on the case’s personal connections. Mutsuo Koshikawa’s identity as Shunichi Watabe is not, by itself, extraordinary to a long-serving detective; what unsettles Kaga is that the suspect is also someone he knows, alongside a victim connected to him through a different part of his life. Matsumiya agrees that Kaga cannot remove Hiromi from the list of suspects simply because the convergence feels like one coincidence too many. Their exchange presents the cousins as partners able to acknowledge personal stakes without allowing them to settle the evidence.

Inherited Counsel and Persistence

While looking for a taxi with Kaga, Matsumiya recalls one of Takamasa’s favorite sayings: “It’s your willingness to explore blind alleys, that’s what decides the outcome of a case”. Kaga grins in recognition. The saying joins their professional method to their family history: the late uncle’s words remain active in the choices of the two detectives, not as a guarantee that every lead will pay off, but as an argument for continuing to examine possibilities.

Kaga’s own search for what can still be learned about Yuriko follows the same commitment. He admits that the chance to change the past has long since passed, yet says he still wants to understand the emotional state she was in. Matsumiya’s presence in conversations about that search places their cousin relationship at the intersection of inquiry and mourning: he is both a fellow detective and a family member who knows the history behind Kaga’s questions.

Significance

The cousins’ relationship gives the investigation a second register. Their work concerns the identity and connections of people in the case, but their conversations also return to a family shaped by mental distress, absence, and bereavement. Takamasa’s remembered counsel provides a practical principle for their investigations; his grief over Yuriko and his final separation from Kaga show the personal costs that principle cannot resolve. Through Matsumiya, Kaga’s private past is neither isolated from the case nor allowed to substitute for evidence. The relationship holds those strands together: professional cooperation, inherited memory, and the continuing effort to understand people who are no longer there to explain themselves.