When you get right down to it, there are a lot of reasons Naomi Osaka may have decided to use her mother's surname instead of her father's. The first is legal. Japanese law dictates that children born to a Japanese parent and a non-Japanese citizen must use the surname of the Japanese citizen. In Osaka's case, that happens to be her mother, Tamaki Osaka, according to The New York Times.
Osaka might have more personal reasons for going by Osaka professionally, though. Like most athletes, Osaka dedicated much of her childhood to her craft, to the point that her family moved from New York to Florida so she could be around the best facilities in the country. When she reached a certain level, it came time to apply for more funding from the Tennis Association of the United States. The request was denied and Osaka ended up committing to repping Japan instead of the States, according to the Wall Street Journal.
Osaka's father was reportedly the one to encourage her to give up her US Citizenship in order to play for Japan, who was more supportive of the rising star. If Osaka was offended enough to give up her citizenship, it's no surprise she'd go by the name of her Japanese mother rather than that of her American father.
