Everyone in this country will end up with the same surname unless laws are changed

An academic has warned that individual dignity as well as loss of regional heritage is at stake.

Ninety-five per cent of wives take their husband's last name in Japan. Source: AAP / Kimimasa Mayama

All Japanese families will have the same surname by 2531, a new study suggests.

Japan is the only country in the world forcing couples to adopt one family name after marriage, with an exception for those who wed foreign nationals.

In a new study, professor Hiroshi Yoshida projects all Japanese people will be known as "Sato-san", the most common last name, unless the civil code is changed.

Yoshida, a professor of economy at Tohoku University’s Research Center for Aged Economy and Society, argues the current system undermines "individual dignity" and could lead to the loss of family and regional heritage.

"If everyone becomes Sato, we may have to be addressed by our first names or by numbers," he said, according to the Mainichi newspaper.

"I don’t think that would be a good world to live in."

Yoshida has calculated that the proportion of Japanese people named Sato increased 1.0083 times from 2022 to 2023.

He claims that if this rate remains constant, Japan will be a nation of Satos in 500 years.

While opponents of a law change argue separate last names would undermine a family's sense of unity, others highlight the civil code that prohibits individual names is fairly new.

Japanese people didn't always have surnames

Japanese people started to register under a single family name after 1875, when a civil code was introduced to modernise Japan.

At that time only high-ranking nobles and samurai had last names, while in ancient Japan clan names were used.

The practice was reportedly imported from the West, and in 1947 it was changed to allow couples to take either person's name.

However, 95 per cent of wives take their husband's last name.

A recent survey showed 61 per cent of respondents favoured a dual-surname option, according to the Japan Times. Source: AAP / Yoshikazu Tsuno

Support for changing the system has grown among Japanese people, with major political parties supporting dual surnames.

The ruling right-wing Liberal Democratic Party is the only exception. It remains split on the issue.

The government has invested millions to upgrade its systems so the maiden name can appear in brackets alongside the family name on some, but not all, official documents.

A United Nations committee has expressed concern about the prohibition of dual surnames on four occasions, with Japan refusing to budge on the issue.

The most common last names in Japan are Sato, Suzuki, Takahashi, Tanaka and Watanabe.