Princess Aiko, 24, enjoys immense popularity but legally cannot become Emperor
Japan's Imperial Family, the world's longest-running monarchy, faces a survival crisis as only three men are eligible to ascend the throne.
Two of these have already reached their sixties or beyond, leaving the institution's future hanging in the balance.
The crisis comes as Prime Minister Sanae Takaichi, the nation's first female leader, is opposed to allowing women to inherit the crown.
During parliamentary debate earlier this year, Ms Takaichi declared it remained "appropriate to limit eligibility to male descendants of the imperial lineage."
The proposed legislative changes, anticipated to become law this month, offer no pathway whatsoever for princesses to claim the throne.
The prohibition on female emperors is a recent development in Japan's imperial history. Before 1889, eight women had occupied the throne.
That changed when the Meiji-era Imperial House Law formally barred women from succession. In 1947, post-war economic devastation prompted lawmakers to slash royal expenditure by reducing the household's size.
Eleven collateral branches, known as Oke, were severed from the Imperial Family tree, causing the Royal Household to shrink from 67 members to just 16 overnight.
In addition, female royals were required to relinquish their status upon marrying commoners. These twin reforms helped create the succession bottleneck now threatening the monarchy's survival, as the family has produced more daughters than sons in recent decades.
As a solution, the Japanese Government is proposing to bring back descendants of the former royal branches, instead of permitting women to inherit the throne.
Under the planned legislation, the Imperial Family would be permitted to "adopt" unmarried, childless individuals from former collateral lines who are at least 15 years old.
Children born to these adopted members would then become eligible for the throne. Emperor Naruhito, 66, has a 24-year-old popular daughter, Princess Aiko.
However, she remains legally excluded from inheriting her father's position, and any children she might have would similarly be barred from succession.
The current line of succession comprises Emperor Naruhito's brother, Crown Prince Akishino, 60, the crown prince's son, Prince Hisahito, 19, and the Emperor's uncle, Prince Hitachi, 90.
Professor Makoto Okawa, who researches imperial lineage at Chuo University in Tokyo, told CNN: "The idea of excluding women in advance as persons incapable of becoming emperor should be understood plainly as misogyny."
Resident Kana Sakakura added: "I suppose when you really compare it to other countries, it does feel like Japan still has an atmosphere where women taking on leadership roles in society is avoided."
However, Tsuneyasu Takeda, who is descended from a former royal branch, disagrees, arguing that Japanese tradition should not be overturned by "a popularity contest."
