TOKYO -- Common-law marriage refers to a relationship in which couples have not filed for marriage at government offices but are effectively in a partnership akin to a legal marriage. However, common-law couples in Japan face many legal limitations, such as ineligibility for certain public systems and rights.

In common-law marriages in Japan, mothers in principle have sole custody of children. As neither of the partners has the right to inherit as a spouse, if one wants to leave their property to their partner, they must go out of their way to bequeath and leave a will. Even if a common-law partner inherits property, they are ineligible for inheritance tax reductions. Furthermore, it is left to the discretion of medical institutions whether a common-law partner can give consent for their partner's medical treatment.

The situation is similar overseas, where common-law couples are not treated as "family members." In the United States and other major countries, even if a person acquires a visa allowing them to bring family members along, their common-law partner is not permitted to accompany them as a spouse.

Meanwhile, the realities of common-law marriages in Japan remain unclear as there have only been few surveys covering them. According to a 2022 Cabinet Office survey, 355 of the 10,906 respondents, or 3.3%, identified as being in a "common-law marriage" from a list of six options: "legal marriage," "common-law marriage," "living with a partner," "estranged," "bereaved" or "unmarried." Based on this and other surveys, it is estimated that 2 to 3% of Japan's adult population are in common-law marriages, or in the range of several million people by simple calculation.

In a recent Mainichi Shimbun survey targeting major domestic companies, among firms with more than 10,000 workers that responded to a question about the ratio of common-law marriages among married employees, 1.4% of employees at one firm reported being in a common-law marriage.

In a May 2024 survey on 111 people in common-law marriages by Asuniwa, a general incorporated association calling for the introduction of a selective surname system for married couples, 86% said they had not filed for marriage because they did not want to change their or their spouse's surname. Meanwhile, 92% of respondents said they would do so if a selective surname system was legalized.

Some experts point out that the marriage rate in Japan would rise if a selective surname system was introduced. Naho Ida, head of Asuniwa, noted, "Our society should transform to allow for more diverse options."

(Japanese original by Makoto Fukazu, Tokyo City News Department)