The development comes just over a fortnight since world number one Osaka won her second career grand slam at Melbourne Park on Australia Day.
After helping the Japanese win her maiden Grand Slam singles title at the 2018 US Open, Bajin was awarded the first-ever WTA Coach of the Year title.
She also thanked Bajin and wished him "all the best in the future". Bajin thanked Osaka and said he wished her "nothing but the best. Thank you for letting me be part of this", Bajin tweeted in reply.
Osaka, who is scheduled to compete in Dubai next week, began sounding out potential replacements late a year ago, local media reported.More news: Pakistan, India hope to reap investment from Saudi prince's visit
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Osaka hired Bajin in 2017 and enjoyed a meteoric rise during the time they worked together.
Osaka, who withdrew from this week's Qatar Open due to a back injury, has not yet announced a replacement for Bajin.
Osaka became the youngest woman to make her debut at No. 1 since Wozniacki at 20 in 2010 and the first tennis player from Asia to reach the top of the women's or men's tennis rankings. Osaka's Twitter feed lit up in response to her announcement, with several memes expressing widespread disbelief - including a shrugging Barack Obama, a confused Joey from American sitcom "Friends" and a Minions character screaming "WHAAAAT?"