Under Japanese law it's long been illegal for spouses to use different surnames.
In fact, it's the only country in the world that still enforces such a rule for its citizens.
But now there are growing calls for Japan's government to change the system, with activists saying it's a matter of equality, and large firms adamant the policy is a big obstacle to doing business.
A recent study from Tohoku University even projected that every person in Japan could have the surname "Sato" in just over 500 years' time unless married couples are allowed to have separate surnames.
And in March, six couples launched a lawsuit against the Japanese government for the right to use different surnames after marriage.
They argue the current system is unconstitutional.
It is a long-term legal process and the first trial date is still yet to be set.
Two of the plaintiffs Yukio Koike, 66, and his partner Yukari Uchiyama, 56, got married every time their three children were born in order to have joint custody rights — and then divorced.
This was "to respect the personality of each other," according to Mr Koike.
"I've never thought of erasing my name in my life."
One of the other plaintiffs said she and her partner had lived together for 17 years and have brought up a teenage daughter, but without marrying.
"The fact that we are not legally a married couple — even though we've lived together as a family for 17 years — could cause problems such as being unable to become a legal heir, or being unable to provide consent for a surgery, or tax law-related disadvantages," the woman, who declined to be named, said.
Makiko Terahara, the lead lawyer in the case, said the surname lawsuit had some similarities to landmark same-sex marriage cases which she has also worked on.
"Human rights are being violated by the unreasonable exclusion of people from the institution of marriage," she said.
What are the laws in Japan?
Since Japan's civil code was created in the 19th century, it has been a requirement that married couples both use the same family name.
The code was amended in 1947 to remove the stipulation that only the man's surname can be chosen.
But in about 95 per cent of cases, wives in Japan take their husband's surname.
History professor Simon Avenell from the Australian National University (ANU) College of Asia and the Pacific said the patriarchal nature of Japan's civil and family law systems reinforced the existing system.
"Even when Japanese laws were reformed after World War II, the practice continued, mainly due to social convention and gender norms," he said.
Apart from the bureaucratic headache of having to change names on everything from passports to bank accounts, reform advocates say the rules create problems for women with established careers.
And if couples decide not to marry, in order to keep their original or maiden names, it can affect a host of rights including those surrounding children, inheritance and tax.
Same-sex marriage also remains illegal in Japan, despite ongoing court actions to rule gay marriage bans unconstitutional.
Who wants to change the rules?
Calls to allow separate surnames have been growing in recent years.
Human rights activists say it's a matter of equality for all citizens, while big business groups have criticised the rules as burdensome and inefficient.
In February, the head of Japan's most influential business lobby, Keidanren, said the group supported the choice of separate surnames for spouses.
Tokyo-based freelance journalist Waka Konohana has long followed the surname debate — and she noted companies are particularly attuned to costs and administrative errors caused by the current system.
"Errors happen when women keep [using] their maiden names at work while changing their surnames to their husbands' on official documents," she said.
"For instance, the HR office books an overseas flight for a female employee who uses her maiden name only at work, but the passport has her married surname on it, so she gets stopped by immigration, or cannot stay at hotels, or cannot use the passport as an ID on a business trip."
Professor Avenell noted that, in recent years, Japanese businesses have become more proactive in empowering women in the workplace.
"There is a growing sense in the business community that outdated practices and laws, like the same surname requirement, do not reflect the realities of the modern Japanese workplace where more and more women work alongside their male counterparts as equals," he said.
Large, multinational Japanese businesses are also particularly sensitive to global norms.
"They realise that outdated practices in Japan can potentially have a negative impact on their dealings and business activities abroad," Professor Avenell said.
"If Japan is perceived to be a laggard in the area of rights and gender equality, it will also potentially be more difficult for Japanese business to encourage talented workers from abroad, particularly women."
According to Ms Konohana, Japan remains a socially conservative society and the issue isn't always front-of-mind for feminist activists.
"This is the oldest issue for Japanese feminists. But the issue of abortions and morning-after pills is equally as big an issue," Ms Konohana said.
Ms Konohana said she thought the Japanese public was more likely to be persuaded by the ease of doing business argument, rather than the human rights justification.
"The human rights and equality approach has never worked, even though the movement has existed since the 1970s.
"A more pragmatic approach can be more effective, so big business groups like Keidanren have started promoting it for the first time this year."
Will everyone in Japan be called Sato?
According to research by Hiroshi Yoshida, a professor of economy at Tohoku University, everyone in Japan could have the last name Sato by the year 2531 unless the system is changed.
Approximately 1.5 per cent of the population have the surname Sato, making it the most common surname in Japan.
Ms Terahara said the research could help show the "irrationality" of the current legal system, but noted the main issue with the current system is that "the human rights of name, freedom of marriage, and equality are being violated."
Professor Avenell said it was likely the modelling, commissioned by the Think Name Project campaign, was done "half tongue-in-cheek".
"True, if current practices continue all Japanese may end up being called Sato," he said.
"The larger point he was trying to make, however, is that the lack of choices such as surname, especially for women, will merely contribute to a Japan lacking the diversity it needs to thrive into the future.
"The issue is not only about surnames, it also connects to other fundamental questions about supporting young people to raise families while they build their careers."
Changing times
The surname debate has ebbed and flowed over the past 50 years, with multiple pro-reform lawsuits filed in more recent times.
Japan's Supreme Court has twice, in 2015 and in 2021, ruled the civil code and family registration laws constitutional — but also urged parliamentarians to discuss growing calls for flexibility.
Backers of the current system say having a single family name is important to promote family ties and that efforts to change the rules are an attack on traditional values.
Professor Simon Avenell said young people now live in a remarkably different Japan to that of their parents and grandparents.
"During the 1970s and 1980s it was common for the man to be the breadwinner and the woman to stay at home raising the children and looking after elderly parents," he said.
"Simply surviving in the Japan of today requires both partners to work and maintain the home front collectively.
"In this changed socio-economic context, it makes more sense for many couples to want to maintain different surnames."
Japanese citizens are also marrying much later in life compared to earlier decades, so couples have more established lives before getting married.
"For these people, changing their surname seems like an unnecessary interruption. For some it also amounts to a loss of identity," Professor Avenell said.
Reform advocates like Ms Terahara said the mood for change has only grown.
She noted that opinion polls showing the percentage in favour of reform "continues to increase", reaching "70 to 80 per cent" in recent surveys.
Will the system change anytime soon?
Professor Avenell said it's hard to know when the law will change, but noted it may be sooner rather than later.
He said Japan's changing demographics — a rapidly aging society and fewer young people — meant more women would need to participate fully in the workplace.
The Japanese government was also sensitive to pressure from the business lobby, he added.
But barriers remain.
"The Japanese ruling party, the Liberal Democrats, is still controlled by middle-aged and elderly men, many of whom cling on to rather outdated values and gender stereotypes," Professor Avenell said.
"Female numbers in the parliament are comparatively low and the situation is worse in terms of female cabinet representation, so there are institutional impediments to legal reform."
The Japanese parliament, the Diet, has the legislative power to reform the system by itself.
But if the Diet chooses not to act, the legal case is expected to take a number of years.
"The Diet should immediately amend the law to solve this problem, but unfortunately that is not expected to happen — that is why we had to file the lawsuit," Ms Terahara said.
"If the Supreme Court rules in this case that the current legal system violates the constitution, the Diet will be forced to amend the law."
"It is expected to be three to five years before the Supreme Court makes its decision."
ABC/AFP
