The development comes just over a fortnight since world number one Osaka won her second career grand slam at Melbourne Park on Australia Day.
The Japanese player captured her first Grand Slam crown by stunning Williams at last year's US Open in a final remembered as much for the American's astonishing rant at the chair umpire following a coaching violation. I wish you nothing but the best as well.
The 21-year-old made the announcement on Monday on her Twitter handle and thanked Bajin for his work.
Bajin became the first recipient of the WTA Coach of the Year award after helping Osaka take her game to new heights in a breakthrough 2018.
She also thanked Bajin and wished him "all the best in the future". What a ride that was. "Thank you for letting me be part of this" he tweeted.
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Rappers Post Malone ("Beerbongs & Bentleys") and the absent Drake's best-seller "Scorpion" are also vying for the top prize. Kendrick Lamar , Drake , and Childish Gambino all reportedly declined to perform at the show.
Osaka hired Bajin before the 2018 season.
An ex-ATP tour player, Bajin won 13 Grand Slams while in the Serena camp, including all four major tournaments and a hat-trick of Wimbledon and US Open titles in a partnership that lasted from 2008 to 2015.
Osaka withdrew from this week's Qatar Open, citing a back injury.
She was born in Japan - her mother is Japanese, her father is Haitian - and moved to the United States when she was 3.