Hiramoto made his professional debut against Yuki Ishikawa at K-1 World GP 2015 -60kg Championship Tournament on January 18, 2015.

[9] Hiramoto faced the one-time Krush lightweight title challenger Minoru Kimura at K-1 World GP 2015 Survival Wars on September 22, 2015.

[11] After suffering his first professional loss, Hiramoto fought Massaro Glunder at K-1 World GP 2015 The Championship on November 21, 2015.

Sasaki earned his place in the finals with decision victories against Hisaki Higashimoto and Takayuki Minamino.

[19] Hiramoto faced the WMPF World Super Lightweight champion Gonnapar Weerasakreck in the tournament semifinals.

[20] Hiramoto faced the Wu Lin Feng lightweight champion Wei Rui in the tournament finals.

[21] Hiramoto was scheduled to face Umar Paskhaev at -1 World GP 2017 Super Welterweight Championship Tournament on June 18, 2017.

[22] Hiramoto was scheduled to fight a rematch with Daizo Sasaki at K-1 World GP 2017 Heavyweight Championship Tournament on November 23, 2017.

[24] Hiramoto was scheduled to face the three-time K-1 lightweight Grand Prix winner Kaew Weerasakreck at K-1 World GP 2018: K'FESTA.1 on March 21, 2018.

[4] Hiramoto was ranked as a top ten featherweight according to Combat Press from April 2018[29] until July 2020,[30] when he transitioned to mixed martial arts, and signed with Rizin.

[32] Hiramoto made his professional mixed martial arts debut against Kyohei Hagiwara at Rizin 26 on December 31, 2020.

[43] Hiramoto faced Mikuru Asakura at Super Rizin 3 on July 28, 2024, under "Last Man Standing" rules, with a symbolic belt on the line.