[citation needed] On December 26, 2020, at "Kakeru Holdings presents A-SIGN.BOXING" held at the Sumida Ward General Gymnasium, he fought Aso Ishiwaki for the Japan Super Lightweight Youth Championship, and won by TKO in the third round in 2 minutes and 50 seconds.
[5] On July 17, 2021, he defended his title against Kaiki Yuba, the Japanese lightweight youth champion, at the Fujimori Gymnasium in Hachioji City, and won by KO in the second round in 2 minutes and 3 seconds, successfully retaining the belt for the first time.
[5] On October 25, 2021, the Japan Boxing Commission (JBC) suspended Sasaki's license for 6 months after he missed weight for the second time, and collected 20% of the fight purse as a fine.
[8] On January 14, 2023, Sasaki fought for the vacant WBO Asia-Pacific welterweight title at Korakuen Hall, defeating champion Ryota Toyoshima by TKO in the first round in 1 minute and 56 seconds.
[9] Sasaki is scheduled to face Shoki Sakai at Ariake Arena in Tokyo, Japan on January 24, 2025.