Family Registry System
The family registry is a system that registers and notarizes the nationality and family relations (birth, marriage, adoption, acknowledgment, death, etc.) of Japanese citizens from when they are born to when they die.
Obtaining a certificate of your family register tells you your place of birth, the name of your (birth) parents, and your relationships with them. It also shows whether your parents were married, and whether acknowledgment was provided by your father. An adopted child may request their former family register from when they were born to when they were adopted under the special adoption system. However, the family registers of the birth parents after the special adoption has been established cannot be requested without a valid reason.
Reference(in Japanese) 法務省「戸籍のＡＢＣ（Ｑ１～Ｑ５）」
Family Register After Special Adoption
When a special adoption is established and the government notified, the adopted child is removed from their birth parents’ family register, and a new family register is created with the adopted child as the head of household. The adopted child then joins the adoptive parent’s family register from this new family register.
Under “Matters of Personal Status” will be written “Article 817-2, Civil Code,” indicating that the child joined the family register through a special adoption.
How to Request a Certificate of the Family Register
The former family register prior to the adoption can be obtained from the city hall that has jurisdiction over your former permanent domicile. You will be required to verify your identity in order to request the family register. If the special adoption has resulted in you having a different name than the one listed in your previous family register, you may be required to present a court order of the special adoption in order to prove that they are the same person.