[1] As an amateur Okubo amassed a record of 145 wins, 18 losses, 3 draws and captured over 40 titles.
During 2021, his last year of competition before turning professional, Okubo won the two most prestigious titles of Japanese amateur kickboxing, the Japan Cup in March and the K-1 Koshien tournament in August.
[4] Okubo made his professional debut on February 27, 2022, at K-1 World GP 2022 Japan against Shohei Nishibayashi.
[9] Okubo made his debut at 53 kg on June 3, 2023, at K-1 World GP 2023 in Yokohama against Ryunosuke Saito.
[16] Okubo faced the two-time K-1 super bantamweight title challenger Masashi Kumura in the final four of the tournament, which was held at K-1 World MAX 2024 on September 29, 2024.
[18] Okubo faced the reigning K-1 super bantamweight champion Akihiro Kaneko in the tournament finals.