Baye McNeil, an author who has lived in Japan for 15 years, said he didn’t understand why the ad would “erase her black features and project this image of pretty much the prototypical anime girl-next-door character.”

Ms. Osaka’s rise into a beloved national figure has been particularly exciting for biracial people in Japan, known as hafus, who have long battled for acceptance, he said.

“Making her look white just tells these people that what they are isn’t good enough,” Mr. McNeil said.

Ms. Osaka was born in Japan to a Haitian-American father and a Japanese mother, and moved to the United States when she was 3. Although she isn’t fluent in Japanese, often responding to questions from Japanese reporters in English, she has tweeted about her love of manga and Japanese movies.

Ranked fourth in the world at just 21, she’s already among Japan’s most accomplished tennis players ever. She became the first Japanese-born tennis player to win a Grand Slam singles championship in September when she defeated Serena Williams in the U.S. Open, a victory that supercharged her celebrity ascent.

That win prompted a cartoon in an Australian newspaper that was criticized for its depiction of Ms. Williams, which many saw as a racist caricature. While most of the condemnation focused on how the Australian cartoonist drew Ms. Williams, critics also noted that Ms. Osaka was depicted with blond hair and light skin.

Black characters aren’t frequently found in anime, but artists in the medium have successfully depicted their skin tones before.