Japan’s New Succession Law Keeps Princess Aiko Off the Throne

Japan’s parliament enacted a historic revision to the 19th-century Imperial House Law on Friday, guaranteeing that only men from the male imperial bloodline can ever sit on the Chrysanthemum Throne. The vote locks Princess Aiko out of succession despite her popularity, betting the monarchy’s future on her 19-year-old cousin, Prince Hisahito, and on royals who do not exist yet.

The revision is billed as a rescue plan for an imperial family that has shrunk from 67 members to 16 since 1947. It forecloses the one succession option that already commands strong public backing: putting a woman on the throne.

What the Revised Imperial House Law Actually Changes

The core rule survives untouched. An emperor’s mother can be a commoner, as Empress Masako is, but only boys born to men carrying the royal bloodline can inherit, a principle first written into law in 1890 and carried into the 1947 statute still in force today.

Friday’s revision adds three things on top of that old rule.

• Adoption – men from the 11 branch families cut loose from the imperial family in 1947 can now be adopted back in, as long as they are male, at least 15 years old, unmarried and childless.
• Marriage protection – princesses can keep their royal titles and duties after marrying commoners, instead of automatically losing imperial status the day they wed.
• No new claim to the throne – adopted men cannot inherit themselves, and neither can a married princess or her children; only a future son born to an adopted man would become eligible.

The adoption clause matters most, since it is the only piece meant to add men to a line of succession that currently has three names on it.

Why Can’t Princess Aiko Become Empress?

Princess Aiko cannot inherit the throne because Japanese law recognizes only male heirs in the male imperial line, and she is a woman. Emperor Naruhito’s only child, now 24, remains legally barred from succession even though she draws bigger crowds and warmer headlines than almost any other working royal.

Public opinion has moved firmly against the ban. A December Yomiuri Shimbun poll found 69% of respondents wanted an empress allowed, versus just 7% opposed. Prime Minister Sanae Takaichi’s government pushed the revision through anyway.

Aiko is not the only princess touched by the old rules. Her cousin Mako relinquished her royal status to marry a commoner in 2021 and now lives in New York, where her husband works as a lawyer. Another cousin, Kako, 31, is still unmarried and faces the same choice.

Aiko’s mother, Empress Masako, a Harvard-educated former diplomat and a commoner by birth, developed a stress-induced condition after Aiko’s birth amid criticism for not producing a male heir. Feminist scholar Chizuko Ueno has since urged princesses to leave palace life the way Mako did, calling the system inhumane and arguing the new measures treat male royals as “stallions” while pressuring female royals to act as “childbearing machines.”

A Female Prime Minister Champions the Male-Only Line

Prime Minister Sanae Takaichi, Japan’s first woman to hold the office, has become the public face of a law that keeps women off the throne. Ueno called that pairing absurd, writing that “it’s very ironic that the first female prime minister herself is the leading proponent of the obsession with male-succession.”

Takaichi has defended the rule publicly. She told fellow lawmakers that “the unparalleled historic fact that the imperial line has been maintained through the male line for 126 generations is the foundation for the emperor’s authority and legitimacy.” In parliamentary debate, she said it remained “appropriate to limit eligibility to male descendants of the imperial lineage.”

The push gained momentum after the Liberal Democratic Party’s landslide win in February’s general election, which emboldened conservatives who had stalled succession reform for two decades.

It’s a declaration to prevent female monarchs and to defend the male-lineage at all costs. They cannot say it’s male chauvinism, so they call it tradition.

Hideya Kawanishi, a Nagoya University expert on monarchy, made that assessment of Friday’s revision.

Five Men, Sixteen Royals, One Teenager

Japan’s imperial family has 16 adult members and no children at all. Just five of the adults are men, and one of them, Naruhito, already holds the throne rather than waiting in line for it.

That leaves three eligible heirs. First is Crown Prince Akishino, Naruhito’s younger brother, who is in his sixties. Second is Akishino’s son, 19-year-old Prince Hisahito, a university student. Third is the emperor’s 90-year-old uncle, Prince Hitachi.

The family’s members range in age from 19 to 91, according to Imperial Household Agency data compiled by Nippon.com. Hisahito is the only member of his own generation who can inherit; his cousins Aiko and Kako cannot, no matter how the public feels about it.

Postwar Purges Set the Stage for Today’s Shortage

The shortage traces back to 1947. As Japan rebuilt after the war, occupation authorities and the new constitution stripped 11 collateral branches of royal status, cutting 51 people loose and shrinking the family from 67 members to 16 almost overnight.

Those 51 people were not close relatives. They had split off from the main imperial line many generations earlier, according to testimony from Imperial Household Agency official Yoshimi Ogata to a parliamentary session this year.

Before 1947, the family had a built-in solution: concubines. Nearly half of Japan’s 125 emperors were born to concubines, a practice a 2005 government panel report described as leaving them “of illegitimate descent.” The practice ended under Emperor Taisho, Naruhito’s great-grandfather, roughly a century ago.

A 2005 government proposal would have allowed female monarchs. It was drafted, then shelved within months of Hisahito’s birth in September 2006.

The Adoption Plan Fixes Nothing for a Generation

The math is the problem. Even if a former royal family agrees to hand over a son, that adopted man cannot inherit the throne himself. Only a son he has after joining the family would be eligible, meaning the adoption clause cannot produce a new heir for at least a generation, and only if it works at all.

Seiichiro Noboru, a former Japanese diplomat with ties to the imperial family, said a simpler fix was sitting in plain sight. “The crucial point is that if a female emperor were recognized, we wouldn’t need to resort to such a complex adoption line,” he said.

Cartoonist Yoshinori Kobayashi, who has campaigned for Aiko’s succession, was blunter. “Who wants the son of an adoptee who nobody knows to be emperor instead of Aiko?” he asked.

Even backers of the plan doubt anyone will step forward. An employee attached to one of the former royal branches told Kyodo News that entering the imperial family means giving up an ordinary career, asking, “Will someone with that resolve really come forward?”

Hisahito, for his part, is a biology student at the University of Tsukuba who joined the university’s badminton club and has co-authored research on dragonflies. That ordinary campus life sits awkwardly next to the weight the law now places on him alone.

• What we know: The revised law passed both chambers of parliament, keeps the throne closed to women, and lets the family adopt eligible men from the 11 branches cut loose in 1947.
• What we know: Adoptees must be male, at least 15, unmarried and childless, and princesses who marry commoners can now keep royal titles while their spouses and children remain commoners.

• Unconfirmed: Whether any eligible men from the 1947 branches actually want to join the imperial family, and how soon an adoption might happen.
• Unconfirmed: What happens after Hisahito’s generation, a question a 2022 government panel said was too early to answer.

Hisahito, any future adoptees and their wives will carry outsized pressure to produce sons, Kawanishi said. There is also concern in Tokyo that the push could unsettle Emperor Emeritus Akihito’s legacy, built in part on making amends for Japan’s role in the Second World War.

Frequently Asked Questions

Who Is Next in Line After Prince Hisahito?

Prince Hitachi, the 90-year-old younger brother of Emperor Emeritus Akihito, is third and last in the current line of succession. A government panel examined the succession question in 2022 and set aside what happens once Hisahito’s generation passes, calling that discussion still premature.

Can Any Princess Become Empress Under the New Law?

No. The revision contains no scenario in which a princess or her children could ascend the throne. Princesses can keep royal titles and duties after marrying commoners, but their spouses and children are entered into a separate family register as ordinary citizens, not the imperial genealogical record.

Has Japan Had a Female Emperor Before?

Yes, eight women have reigned as monarch, most recently Empress Gosakuramachi from 1762 to 1770. Each inherited through her father’s bloodline and none passed the throne to her own children, a pattern conservatives cite as proof female reigns were always meant to be temporary.

Who Can Be Adopted Into the Imperial Family?

Candidates must be male, at least 15 years old, unmarried and childless, and must descend from one of the 11 branch families removed from the imperial family in 1947. Those branches split from the main line at least 36 generations ago, roughly 600 years back, according to Imperial Household Agency official Yoshimi Ogata.

Do Japanese Voters Support a Female Emperor?

Support has grown for years. Opposition to a female monarch fell from 13.5% in a 2019 Kyodo News poll to just 7% in a Yomiuri Shimbun poll published in December, while most respondents in the newer survey backed changing the law.

Has Japan Faced International Pressure Over the Rule?

Yes. The United Nations Committee on the Elimination of Discrimination against Women recommended in a 2024 report that Japan revise its male-only succession rule to meet gender equality standards. Friday’s revision left that rule fully in place.