TOKYO >> If anyone can stir Japanese national pride at this moment, it is Naomi Osaka.

The world’s No. 1-ranked player in women’s tennis, Osaka is among the biggest stars in Japan, splashed across television programs and advertisements for Nissan cars and Citizen watches. As a mixed-race person, she has also helped prompt a discussion about how Japanese see their country.

But a looming deadline — Osaka’s 22nd birthday in October — has raised the question of whether she can continue to represent Japan on the international tennis circuit, where she has given the country bragging rights on the world sports stage.

Osaka, whose mother is Japanese and father is Haitian-American, has citizenship in both Japan and the United States. Under Japanese law, dual citizens must choose between the two nationalities by the time they turn 22.

That legal clause has left fans and commentators trying to guess whether Osaka will pick citizenship in Japan, the country of her birth, or the United States, where she has lived since she was a young child.

The choice facing Osaka comes as Japan is under pressure to loosen its entrenched insularity. Japan has long prized racial purity, seeing a largely homogeneous population as crucial to social cohesion. But with the country’s population declining and employers increasingly desperate for workers, its legislature passed a law in December to admit more guest workers, starting this month.

Osaka’s case, along with the new influx of foreigners, could exert new pressure on the government to begin to bring Japanese citizenship laws in line with those in the roughly three-quarters of countries, including the United States, that allow dual citizenship.

For now, though, Osaka has a decision to make. When asked by reporters which nationality she intended to choose, she responded with trademark feistiness.

“I’m pretty sure it’s obvious,” she said in October. “I’m playing for Japan. Not to be disrespectful or anything, but I don’t really get where the conclusion that it’s a hard choice for me or anything comes from.”

Still, it might be hard to imagine Osaka giving up her American citizenship to keep playing under the Japanese flag. And in reality, she may not have to. Legal experts say the Japanese government rarely enforces the law requiring citizens to choose between nationalities.

The Justice Ministry estimates that about 890,000 Japanese citizens might also hold foreign passports, and the government has never revoked Japanese citizenship from anyone who, like Osaka, was granted citizenship at birth. (Japanese citizens who voluntarily naturalize in another country automatically lose their Japanese citizenship.)

But some analysts warn that because of Osaka’s celebrity, it would be difficult for the government to quietly give her a pass on dual citizenship.

Osaka’s multicultural background has challenged Japan’s notions of national identity, and she has become the most prominent mixed-race and mixed-nationality figure in a country where only 1 in 50 children born each year has a foreign parent. Though she is not fluent in Japanese, she has captivated the country with her whimsical remarks to the news media, as well as her humility in victory.

Her parents decided when she was young that she and her sister, who also played, would represent Japan, partly because the American tennis federation showed them little attention.

Anticipating Osaka’s citizenship choice, Michio Ushioda, former columnist for The Mainichi Shimbun, a daily newspaper, and a professor at Teikyo University in Tokyo, said on Twitter that Japan would fall into a national funk if she elected U.S. citizenship over Japanese.

“The disappointment of the Japanese at that time would be great,” Ushioda wrote, even suggesting that Japan’s current administration would collapse if Osaka competed for the United States in the Olympics.

Under International Olympic Committee rules, competitors must be nationals of the countries they represent. Similarly, under International Tennis Federation rules, Osaka could not play for Japan if she gave up her Japanese citizenship.

Legal experts say Japanese law provides a loophole through which dual citizens can effectively retain both nationalities. The law requires only that a Japanese citizen “endeavor to renounce” foreign nationality, a phrase that can provide just enough wiggle room for citizens to hold on to an extra passport.

“Many people misunderstand the law and feel threatened that they have to choose a nationality,” said Yasuhiro Okuda, a law professor at Chuo University.

Until 1985, Japan granted citizenship only to children whose fathers were Japanese. When it changed the law — a move it made under pressure from international critics who said the rules discriminated against women — the government added the clause stipulating that children with dual citizenship would have to choose between their passports by the time they turned 22.

Analysts say Japan’s law makes little sense in a modern world filled with multicultural citizens like Osaka.

For older generations, opening Japan to a pool of newly naturalized citizens could generate a considerable political backlash.

But younger Japanese are growing more accustomed to living and working with international neighbors and colleagues.

“Young people in their 20s now are much more familiar with foreigners or so-called ‘hafu,’” said Satoko Takeda, visiting researcher at Osaka University of Economics and Law, using the Japanese term, from the English word “half,” to describe those of mixed-race descent like Osaka. “They are different from previous generations. I think there is hope.”