Osaka grew up in the US but told NHK that it gives her "a special feeling to try to go to the Olympics to represent Japan".
Japanese law states those with dual citizenship must select one before turning 22.
Osaka, who has a Japanese mother and a Haitian father, told NHK she has completed an administrative step to obtain Japanese citizenship ahead of her birthday next week.
She told Japanese public broadcaster NHK that it gives her "a special feeling to try to go to the Olympics to represent Japan".
And while Japan has largely embraced Osaka, she still faces some indignities. Osaka won her first singles title since the Australian Open in January by beating Pavlyuchenkova 6-2, 6-3 in the final. "I think that will be one of the most memorable things that ever happens to me".
Osaka rose to prominence a year ago after she managed to beat US tennis legend Serena Williams in the final of the 2018 US Open.
Osaka represents Japan on the WTA Tour and in the Fed Cup.
In July, in an interview with the International Tennis Federation, she said: "Winning gold in Tokyo is something that I have dreamed about".
She also said she does better in very high-stakes moments, so she has high expectations for herself in the Tokyo Olympics.