Amid the excitement of Naomi Osaka winning the women's title at the U.S. Open tennis tournament last weekend, some in Japan are wondering whether she will continue to compete for their country at the 2020 Tokyo Olympics.

The 20-year-old has dual nationality — Japanese and American — and under Japanese law will have to choose one by the time she turns 22 on Oct. 16 next year, although that regulation is rarely enforced. While the Justice Ministry officially has the right to warn dual nationals to choose one, it has never done so, and the Foreign Ministry has said it does not track dual nationals.

"I'm so proud of her," said Hiromi Shibata, a 32-year-old Tokyo resident and tennis fan. "It doesn't really matter what flag she represents because that doesn't change the fact that she has Japanese heritage, but deep down I'm hoping she will play for Japan at the next Olympics."