Naomi Osaka’s Breakthrough GameNaomi Osaka’s Breakthrough Game

The temperature in Boca Raton had soared above 90 degrees, but on a side court at the Evert Tennis Academy, Naomi Osaka was just digging into one of her last training sessions before the summer hardcourt season. Wearing leggings and a tank top — her magnificent mane of frizzy blond-tinted hair emerging from the back of her Adidas cap — the 20-year-old smacked crisp topspin groundstrokes with her coach, Sascha Bajin, a German of Serb descent best known for working as Serena Williams’s hitting partner for eight years. On the sideline, Osaka’s Japanese mother, Tamaki, sat in the shade in a denim jumpsuit and sunglasses, her daughter’s miniature Australian shepherd sitting by her feet. Pacing on the grass alongside the court was her Haitian-born father, Leonard Francois, a taciturn man in a baseball cap who trained her from age 3 and still tracks nearly every shot she hits.

Some version of this simple scene — dutiful parents, a gifted child, the metronomic thump of a ball — plays out every day at tennis courts and sports fields across the world. Only in this case, the parents’ unlikely union has led to the emergence of one of the most intriguing young stars in sports today: an athlete who has grown up in one place (the United States), represents another (Japan) and, for some, symbolizes something as large as the world’s multicultural future. In playing under the flag of an island nation noted for its racial homogeneity, Osaka challenges assumptions about whether and under what circumstances a biracial person might be accepted as truly Japanese. For her part, Osaka, shy and quirky, with a penchant for unexpected candor, seems focused solely on becoming the next Serena. Her ambition, she once told a reporter, was “to be the very best, like no one ever was.” After a beat, realizing that her interlocutor was not tuned to her frequency, she explained: “I’m sorry; that’s the Pokémon theme song. But, yeah, to be the very best, and go as far as I can go.”

On this searing afternoon, Osaka was amping up the velocity of her shots. “Ninety seconds!” shouted her conditioning coach, Abdul Sillah, looking at his stopwatch. Osaka and Bajin were halfway through their first three-minute drill, a baseline rally that lasts about 10 times longer than an average exchange in a match. The drill is meant to make the legs and lungs burn without affecting the pace and placement of the athlete’s groundstrokes. It also happens to goad Osaka’s competitive pride. After about 80 shots, by my count, neither she nor Bajin had missed. As the clock slogged on — “Two minutes!” Sillah said, then “Two and a half minutes!” — it was clear that each was trying to make the other crack. Osaka let out a shriek as she scrambled to return one of his deep shots down the line. As the last seconds ticked away, Osaka crushed a forehand crosscourt for a winner. “I hit with Serena almost every day for eight years, and Naomi’s weapons are just as big,” Bajin says. “She’s not afraid of center stage, either, and that’s why I believe she has greatness within her.”

As the U.S. Open begins this week, Osaka may be a premature pick to lift this year’s trophy, but the prospect also wouldn’t be entirely outlandish. At 20, she is the youngest woman in the world’s Top 20 — and Japan’s highest-ranked female player in more than a decade. Serena Williams declared two years ago that Osaka was “very dangerous.” So it wasn’t a complete surprise when she put together a spectacular run in March at Indian Wells, in California, demolishing three current or former world No.1s on the way to her first W.T.A. title. Those upsets catapulted her up the rankings, from No. 68 at the end of 2017 to 17 by early August. “Ever since I can remember, I played better against bigger players on bigger courts,” she told me, her high, soft voice a contrast to the ferocity she displays on court. Tsuyoshi Yoshitani, a sports reporter with Kyodo News, says: “Naomi is like no Japanese player ever before. I think she will be the first Japanese player to win a Grand Slam.”