Kumura is a two-time K-1 World Grand Prix finalist, having finished as the runner-up in the 2019 and 2022 super bantamweight tournaments.
[6] Kumura made his professional debut at NJKF IGOSSO REBORN 2014, when he was scheduled to fight Kyosuke Nishida.
Kumura thoroughly dominated the future champion, winning the fight by unanimous decision, with all three judges awarding him a 30-26 scorecard.
[12] Kumura won the fight by knockout, knocking Oiwa down with a left-hook midway through the first round, which left him unable to beat the eight-count.
[18] Kumura beat Phetpangan with a first-round technical knockout, managing to knock his opponent down twice inside of the first round.
Advancing to the semifinals, Kumura beat Samvel Babayan by unanimous decision, and faced the reigning K-1 Super Bantamweight champion Yoshiki Takei in the finals.
[20] Kumura successfully defended his title with a majority decision victory, with two of the judges scoring the bout 29-28 in his favor.
[22] Kaneko previously fought and beat Masashi's brother Shuhei Kumura by an extra round decision at K’FESTA 2.
[35] He made quick work of Kiyama, stopping him with a lead leg body kick 84 seconds into the opening round.
Kumura made quick work of Sasaki, as he knocked him down twice by the 1:37 minute mark of the opening round, which resulted in an automatic technical knockout victory for him.
[36] Kumura advanced to the tournament finals, where he faced the former Krush Super Bantamweight champion Akihiro Kaneko.
[39] At a K-1 press conference held on June 29, 2022, it was announced that Kumura would fight at K-1 World GP 2022 Yokohamatsuri on September 11, 2022.
[40] At a second press conference, held a month later, it was revealed that Kumura would face the two-weight Lumpinee Stadium and three-weight Channel 7 champion Kompetch Sitsarawatsuer in a 56 kg catchweight bout.
In the post-fight interview, Kumura called out the reigning K-1 super bantamweight champion Akihiro Kaneko for a fight in March of the next year.
[44] Kumura faced the RISE Bantamweight champion Masahiko Suzuki at K-1 World GP 2023: K'Festa 6 on March 12, 2023.
[46] Kumura challenged the K-1 Super Bantamweight titleholder Akihiro Kaneko at K-1 World GP 2023: ReBOOT～K-1 ReBIRTH～ on September 10, 2023.
[52] Kumura faced the former Krush Flyweight (-51kg) champion Rui Okubo in the tournament semifinals at K-1 World MAX 2024 on September 29, 2024.