Japan’s Civil Code three-hundred-day rule

Japan’s Civil Code three-hundred-day rule treats a child born within 300 days of a divorce as the former husband’s child. In the novel, the presumption is more than a question of legal parentage: when it leads a mother to withhold a birth notification, a child may have no family-register record and become invisible to the state’s systems for recognizing life and death.

The presumption and its consequences

The rule’s practical effect emerges through a case brought to lawyer Kido’s colleague Nakakita. Women who had divorced after domestic violence and soon had children with new partners sometimes refrained from submitting birth notifications because the law assigned parentage to their former husbands. As a result, some children entered society without family registers, despite meeting the conditions for Japanese citizenship. If such a child died in the tsunami, the state’s records would not register either the birth or the death; the person’s entire existence could be absent from official accounting.

The problem therefore connects intimate family circumstances to administrative recognition. A legal presumption about a former marriage can shape whether a child is recorded as belonging to a family, while a missing record can determine whether public institutions can count that person at all. The novel sets this domestic legal problem beside the vanished tsunami victims to show how the absence of documentation can become an absence in the state’s account of the living and the dead.

Kido’s investigation and the missing identity

The rule becomes a lead in Kido’s attempt to identify the man who lived and died as Daisuké Taniguchi. The man’s official records appeared consistent: authorities had accepted his marriage and death notifications, and he had used a driver’s license and health-insurance card and made pension contributions. Yet Kyoichi Taniguchi, the real Daisuké’s brother, had identified the deceased man as someone else after seeing his photograph.

After hearing Nakakita describe children lacking registers, Kido considers whether the impostor, X, might have been unregistered. If X had no public record, Kido reasons, the real Daisuké might have taken on X’s identity in an exchange of family registers. The possibility also changes the stakes of Kyoichi’s suspicion that Daisuké was murdered: if the missing man had been legally absent from the outset, a discovered body might be treated as unidentified, while a body lost in the tsunami could leave almost no physical evidence to pursue. The rule does not establish what happened to either man, but it opens a route by which Kido can understand how an identity might disappear from official records.

Family registers as instruments of recognition

The novel places the three-hundred-day problem within a longer history of the Japanese family register. Nakakita explains that the system dates to the Ritsuryo-era bureaucracy and later expanded in the Edo period to include information such as birth, marriage, adoption, address, occupation, and death. Because it assumed a person’s attachment to a place, it became less suited to a society in which freedom of movement was recognized; the modern register introduced in the Meiji period also encouraged some people to discard or falsify records to evade conscription and taxes. Across these changes, people remained outside the register’s account.

The legal issue is therefore part of the novel’s wider concern with the difference between a person and the records that purport to establish who that person is. Kido’s own experience as a third-generation Zainichi person who became a naturalized Japanese citizen in high school gives particular weight to Nakakita’s observation that people excluded from the register could be denied full recognition within the nation. Nakakita adds that the government increasingly manages identity through residence certificates and the My Number system, and suggests that integrating systems could make the family register redundant. Kido counters that easier administrative linkage might also make identity exchange easier, until biometric identification made the system difficult to evade. The conversation leaves the rule in a larger tension: records can grant recognition, exclude people, and provide both the means to trace identity and the means to manipulate it.

The rule beside Rié’s legal crisis

Rié’s own case does not turn on the three-hundred-day presumption, but it echoes the novel’s concern with how legal records define family. After learning that X had lived as Daisuké Taniguchi, Kido filed petitions at the Miyazaki Family Court to correct the linked family registers. The court was asked to cancel the record of Daisuké’s death, remove the supposed husband from Rié’s register, and restore her maiden name, Takemoto; annulling the marriage on grounds of error would also make Hana legally illegitimate. Because the identity question was complex, the court required Rié to appear and requested DNA evidence. Kido collected hair, nail clippings, an electric razor, and a toothbrush from X’s belongings as samples.

These proceedings distinguish the rule’s direct application from its thematic role. The three-hundred-day presumption concerns how a child’s parentage is assigned after divorce; Rié’s petition concerns an annulment and the correction of a register after impersonation. Together, however, they show how official classifications can alter a child’s legal status and a parent’s recorded identity, even when the underlying personal relationships are more complicated than the documents allow. The novel’s concern is not simply whether a register is accurate, but what becomes possible—or impossible—when institutions treat its entries as the measure of a life.