Hiromasa Ougikubo began his mixed martial arts career in 2005, as an amateur in Shooto.
[7] Ougikubo made his professional debut with Shooto in 2006, when he defeated Nobuhiro Hayakawa by a unanimous decision.
Hiromasa would win the fight in the third minute of the third round, by way of a rear naked choke, in what was considered, at the time, a major upset.
Horiguchi would defend or reverse the takedowns, deliver ground and pound from the guard, and would eventually submit Ougikubo in the second round.
Proceeding to the finals against Czar Sklavos, Ougikubo came out the victor after 25 minutes, being declared the tournament champion, by a clear unanimous decision.
This gave him his second chance at Shooto gold, as he was set to fight the bantamweight champion Masaaki Sugawara.
He would force wrestling exchanges with Pantoja, working from his opponents guard, grinding away a unanimous decision win.
[42] Ougikubo faced Takeshi Kasugai in the opening round of the Bantamweight Grand Prix at Rizin 28 on June 13, 2021.
[47] He won the fight by unanimous decision, and faced Kai Asakura in the tournament finals, which were held during Rizin 33 as well.
[49][50] Ougikubo was booked to face the Road FC Featherweight champion Soo Chul Kim at Rizin 38 on September 25, 2022.
[51] Although he was scrambled from start to finish, he was outnumbered by Kim's punches and suffered two facial fractures, resulting in a 0-3 unanimous decision loss.
[52] Moving down to Flyweight, Ougikubo faced Kyoji Horiguchi at Bellator MMA vs. Rizin on December 31, 2022.
[54][55] Stepping in as a replacement for an injured Kai Asakura, Ougikubo faced former Bellator Bantamweight Champion Juan Archuleta for the vacant Rizin Bantamweight Championship title on July 30, 2023, as part of the Bellator MMA x Rizin 2 card.
[57] Ougikubo faced John Dodson on December 31, 2023, at Rizin 45,[58] and won the bout via unanimous decision.
[59] Ougikubo faced Makoto Takahashi on July 28, 2024 at Super Rizin 3, and won the bout via unanimous decision.