Koseki

In the case of a child born out of wedlock to a Japanese father who has acknowledged the child, even if the child holds a foreign nationality, it is still possible to add the acknowledgment to the father's family register after the child reaches adulthood. In the case of a child born abroad to a Japanese mother, if a birth report and a notification of intent to retain Japanese nationality were not submitted to the Japanese government within three months of birth, and the child holds a foreign nationality, it becomes impossible to add the child to the mother’s family register after the child becomes an adult. While a child acknowledged by a Japanese father may be added to the father’s koseki even after reaching adulthood, a child born to a Japanese mother who failed to submit the required documents within the legal timeframe cannot be added once the child has become an adult.This discrepancy in treatment arises despite both children being born to a Japanese parent, and the legal reasoning for this difference is as follows: Submitting a birth notification to the Japanese government within three months of birth is a constitutive act, meaning it is required to establish the child’s legal status as a Japanese national in the family register.If the child fails to file a notification of intent to retain Japanese nationality within this period, they lose their Japanese nationality under Article 12 of the Nationality Act.Since the koseki is a legal register that records the personal status of Japanese nationals (Article 10 of the Family Register Act), a child who is no longer considered Japanese due to the loss of nationality cannot have their birth information recorded in the register after the deadline. Therefore, in case 2, if the child is still a minor, there may still be difficult but possible administrative remedies to retain or restore Japanese nationality. However, once the child becomes an adult, unfortunately, there is no administrative remedy available. (This limitation applies only to those who have acquired a foreign nationality from their birth; in cases where the child has become stateless for some reason, the handling will differ.) In contrast, in case 1, regardless of whether the child holds a foreign nationality, the act of acknowledgment by the Japanese father is a valid legal action. Even if the acknowledgment was established under foreign law, it is recognized as effective under Japanese law.Therefore, the acknowledgment can be submitted to Japan as a notification of reportable facts, and the acknowledgment details can be added to the father's koseki even after the child becomes an adult. As shown above, while the two cases (in which a child, who holds foreign nationality, is born to a Japanese parent, but the child’s existence is not recorded in the Japanese parent’s koseki (family register) until after reaching adulthood) may seem similar, the legal treatment is substantially different.As a result, in case 1, the child’s existence can be added to the father's family register even after adulthood, whereas in case 2, the child cannot be added to the mother’s family register once they have become an adult.

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Addition of a Child to a Japanese Parent’s Family Register (Koseki)