Early career Kawahara made his professional debut at Pancrase Osaka on July 26, 2015, against Tsukasa Zenji. The fight ended in a draw, as neither fighter achieved a stoppage inside the time limit. He won his next fight against Tatsuki Ozaki, which was likewise contested under the
Pancrase banner, by unanimous decision. He moved briefly to
DEEP, where he made his promotional debut against Icho Tomonaga at DEEP Osaka Impact 2016. He won the fight by TKO, after just 16 seconds. He next fought Magisa at DEEP Cage Impact 2016 in Osaka, and won the fight by an armbar in the second round. Returning to Pancrase, Kawahara suffered his first professional loss to Takuya Goto, by split decision. He rebounded from this loss with a first-round TKO of Noriyuki Takei at DEEP Osaka Impact. He was then scheduled to fight Yutaro Muramoto at DEEP Cage Impact 2017, whom he beat by a second-round TKO. His next fight was against Yuya Kodama at DEEP 80. The fight ended in a no-contest, as Kawahara landed an accidental low blow which rendered Kodama unable to continue. His next fight against Yutaro Muramoto, at DEEP 85, ended in a majority draw. Following this four-fight unbeaten streak, Kawahara was scheduled to fight
Haruo Ochi at DEEP 88 for the
DEEP Strawweight title. Ochi won the fight by unanimous decision. After his failed title bid, Kawahara was scheduled to make his
RIZIN debut at
Rizin 16 - Kobe, when he was scheduled to fight Takaki Soya. Soya won the fight by a first-round TKO.
DEEP title reign Kawahara was scheduled to fight Jun Nakamura in a Pancrase and DEEP cross-promotional event, in a DEEP Strawweight title eliminator. Kawahara won the fight by a first-round TKO. After beating Nakamura, Kawahara was scheduled to once again challenge for the
DEEP Strawweight title, in a rematch with
Haruo Ochi. He beat Ochi by a second-round submission, locking in a rear-naked choke in the dying seconds of the second round. It was the highest profile victory of Kawahara's career up to that point. Following his win against
Haruo Ochi, and prior to signing with
ONE Championship,
Fight Matrix ranked him as the second best strawweight in the world.
ONE Championship Kawahara then made his
ONE Championship debut at
ONE Championship: Unbreakable, being scheduled to fight Lito Adiwang as a late notice replacement for Hexigetu. Adiwang won the fight by a second-round TKO. Kawahara was booked to face Danial Williams at
ONE 156 on April 22, 2022. He lost the fight by unanimous decision. ==Championships and accomplishments==