Introduction
“Please obtain the current koseki of the decedent.”
We occasionally receive such requests from probate genealogists overseas. However, this request does not work in Japanese inheritance practice. This is because Japan requires all consecutive koseki from the decedent’s birth to death.
In some cases, more than 10 koseki may be necessary. This is due to the unique characteristics of Japan’s koseki system.
If you were to apply for a koseki at a Japanese city hall, the city hall employee would say, “This is for inheritance purposes, right? One copy isn’t enough. Is that okay? The fee isn’t enough to obtain the koseki necessary for inheritance.” You would be confused by this misunderstanding.
Also, there is no guarantee that city hall employees won’t accidentally fail to issue the koseki along the way. You need to be able to check yourself that there are no missing koseki.
Obtaining koseki is very easy
Japanese citizens can obtain koseki (戸籍謄本、family registers) listing all heirs necessary for inheritance procedures by simply submitting one application form with just six items – address, name, date of birth, honsekichi (本籍地、registered domicile), first registrant in the family register, and purpose of acquisition – waiting 30 minutes to 1 hour, and paying a few thousand yen to the city office. City office staff will quickly print the necessary koseki. Koseki attachment lists heirs’ current addresses.
Why Are Multiple Koseki Necessary?
Japanese inheritance procedures require all koseki documenting the decedent from birth to death, as well as koseki tracing from the decedent’s records to each heir’s current status. This is due to specific circumstances related to how Japanese koseki are created and how family relationships are understood through them.
Why Koseki from Birth to Death Are Required
In Japanese inheritance practice, submission of all consecutive koseki proving all status changes from the decedent’s birth to death is required. This is to verify the following matters:
- Marital relationships: Presence of current spouse, history of past marriages and divorces
- Parent-child relationships: All legitimate children, illegitimate children, and adopted children
- Recognition: Whether children born outside marriage have been legally recognized
- Confirmation of absence of other heirs: Proof that no other potential heirs exist
- Naturalization: For naturalized citizens, status matters in their country of origin before naturalization must be investigated
Why the “Most Recent Koseki” Alone Is Insufficient
If we consider the time of the decedent’s death as “most recent,” the koseki (or removed koseki) recording the decedent’s death alone may lack the following information:
Omissions due to reformatting: Former spouses or children from previous marriages who were already removed at the time of reformatting are not transferred to the post-reform koseki.
Children with divorced spouses: If a child moved to the mother’s koseki after divorce, the father’s koseki will record the child’s birth but not subsequent status (survival, death, etc.).
Separate koseki during marriage: If a spouse’s surname was chosen at marriage, the person enters the koseki where the spouse is the first registrant. If the person returned to their original koseki after divorce, the existence of children born during the marriage cannot be confirmed without obtaining the koseki from the marriage period.
Basic Structure of Japanese Koseki
Koseki Are Compiled by Family Unit
Unlike birth certificates or marriage certificates issued individually overseas, Japanese koseki are status registration documents compiled by family unit. Each koseki has a designated first registrant (or head of household), identified by that person’s name and registered domicile (honsekichi).
Post-war koseki consist of one to two generations: “married couple and unmarried children.” Members are removed, entered, or new koseki are compiled due to events such as marriage described in the section below. Pre-war koseki consisted of multiple couples and children spanning several generations within the range recognized as family.
What is honsekichi (registered domicile): The honsekichi indicates the local government authority managing the koseki register and consists of a town name and lot number for the convenience of administrative searches. It is separate from the address on the resident register (where one actually lives). Before the war, honsekichi often equaled residential address, but since the establishment of the resident register system, current address and registered domicile have been completely separated. There are also people have never visited their honsekichi because they have moved completely away from it.
Types of Koseki
Koseki transcript (戸籍謄本 koseki tohon): A koseki with current members. Entries are added to the same koseki until all members are removed through marriage, death, transfer of domicile, etc.
Removed koseki transcript (除籍謄本 joseki tohon): A koseki from which all members have been removed. The retention period is 150 years after removal.
Original koseki before reformatting (改製原戸籍 kaisei-genkoseki): When format changes (reformatting) occur due to legal regulations, the koseki preserved in the pre-reform format. Reformatting creates a new format koseki, but entries for persons already removed at the time of reformatting are not transferred to the new koseki.
Evolution of Koseki Formats
Japanese koseki formats have changed through institutional reforms. Major reformattings include:
Pre-war formats (Meiji 19, Meiji 31, Taisho 4 formats): “House” (ie) unit koseki centered on the household head. Three or more generations were sometimes recorded in the same koseki.
1957 Ministry of Justice Ordinance No. 27 format (Showa 32 format): Following post-war Civil Code reforms, “household head” was changed to “first registrant,” establishing the current basic structure of “married couple and their unmarried children” as the unit.
Computerization format (Heisei reformatting): Each municipality sequentially implemented computerization. The format became horizontal writing style.
Events That Cause New Koseki Compilation
The main events that cause one person’s status matters to be dispersed across multiple koseki are as follows:
Marriage: Marriage causes compilation of a new koseki. Depending on which surname is chosen, either the husband or wife becomes the first registrant.
Adoption: Through adoption, the adoptee enters the adoptive parents’ koseki.
Divorce/dissolution of adoption: When a person who changed their surname at marriage returns to their pre-marriage surname, they generally return to their pre-marriage koseki (usually their parents’ koseki). However, a new koseki is compiled if that koseki has already been removed, if the person will be in the same koseki as unmarried children, or if the person requests it.
Reformatting: As mentioned above, entries for persons already removed at the time of reformatting are not transferred to the new koseki. Therefore, both pre- and post-reform koseki must be obtained.
Transfer of domicile (転籍): Moving the registered domicile to a different municipality. Transfer causes compilation of a new koseki, and the previous koseki becomes removed.
Separation (分析): If one wishes to leave their parent’s koseki, they separate.
Unmarried mother’s childbirth: Since koseki consist of two generations or fewer, when an unmarried woman gives birth, a new koseki consisting of two generations (mother and unmarried child) is compiled.
Branch family (分家): A pre-war system for legal establishment of a branch family.
Inheritance of family headship (家督相続): A pre-war system where a new koseki was compiled when the household head retired or died.
Concrete Example: What Koseki Are Needed?
Let’s consider a hypothetical example.
Case: Jiro Yamada (born 1950, died 2024)
Life events:
- 1950: Born into father Taro Yamada’s koseki (honsekichi: 1-23-4 Jujo, Kita-ku, Tokyo)
- 1975: Married Hanako Suzuki (honsekichi:2-345-6 Odori, Chuo-ku, Sapporo City, Hokkaido), Hanako chose “Yamada” surname
- 1976: Eldest daughter Misaki Yamada is born
- 1980: Divorced, Jiro returns to father’s koseki
- 1983: Separated registered domicile to Osaka (honsekichi: 3-4566 Honcho, Yodogawa-ku, Osaka City, Osaka Prefecture)
- 1985: Transferred registered domicile to Osaka (honsekichi: 5-3225 Nishi, Minami-ku, Sakai City, Osaka Prefecture)
- 1994: Koseki reformatted due to computerization
- 2024: Death
Required koseki:
- Father Taro Yamada’s removed koseki (Kita-ku, Tokyo) – Records Jiro’s birth (pre-war format)
- Father Taro Yamada’s original koseki before reformatting (Kita-ku, Tokyo) – Pre-1958 reform format
- Koseki with Jiro as first registrant during marriage (Kita-ku, Tokyo) – Records marriage to Hanako, Misaki’s birth
- Father Taro Yamada’s koseki (Kita-ku, Tokyo) – Jiro’s return after divorce
- Former wife Hanako Suzuki’s koseki compilation (Sapporo City, Hokkaido) – Misaki enters new koseki with Hanako as first registrant
- Koseki with Jiro as first registrant compilation (Kita-ku, Tokyo) – Separation
- Koseki with Jiro as first registrant (Osaka City, Osaka Prefecture) – Transfer
- Jiro’s original koseki before reformatting (Osaka City, Osaka Prefecture) – Pre-computerization
- Jiro’s removed koseki transcript (Sakai City, Osaka Prefecture) – Post-computerization, records death
What If Specific Koseki Were Not Obtained?
If koseki 3 (marriage-period koseki) were not obtained:
- Eldest daughter Misaki’s existence cannot be confirmed
- Cannot confirm whether other children exist
- Heirs cannot be determined
If koseki 5 were not obtained:
- Daughter Misaki’s life or death cannot be confirmed
- If Misaki died, cannot confirm whether she married or gave birth
- If Misaki gave birth and then died, information about Misaki’s children cannot be confirmed
If only the most recent koseki 9 were obtained:
- Divorce history unknown
- Information removed before reformatting (former spouse, children) not included
- Continuity from birth to death cannot be proven
Conclusion
It is a misconception that “one family register is sufficient for inheritance procedures in Japan, which has a family register system.”
Particularly for inheritance cases from overseas, appropriate koseki collection is difficult due to language barriers.
Our institute provides support for identifying necessary koseki, analyzing obtained koseki, and confirming family relationships. Please contact us for details.
