[2][3] Osaki made his professional debut at J-NETWORK J-KICK 2016～Honor the fighting spirits～2nd with a unanimous decision victory over Idomu Tateshima.
He amassed a 10-2-1 record, before fighting Satoshi Katashima for the WMC Japan Super Flyweight title at Muay Lok 2018 Challenge.
[4] In his next fight, at J-KICK 2018～4th～, Osaki fought Masanori Matsuzaki for the J-NETWORK Super Flyweight title.
[10][11] After capturing his third professional championship, Osaki was booked to face Azusa Kaneko in a reserve fight of the 2021 RISE Dead or Alive Tournament, which took place on July 18, 2021.
[13] Osaki was scheduled to face Koudai Hirayama in a tournament reserve match at RISE WORLD SERIES 2021 Yokohama on September 23, 2021.
He won the fight by a first-round technical knockout, after knocking Jyosei down three times by the midway point of the opening round.
They were initially expected to face each other in the semifinals of the 2021 RISE "Dead or Alive" bantamweight tournament, before the fight was cancelled due to Osaki missing weight.
[23] Osaki faced Seiki Ueyama at RISE World Series / SHOOTBOXING-Kings 2022 on December 25, 2022.
Osaki landed an accidental low blow midway through the final round, which rendered his opponent unable to continue fighting and prompted the referee to call for a technical decision.
[33] Lahmar withdrew from the fight on May 7, due to knee and hip injuries, and was replaced by Samvel Babayan.