Early career Hiramoto made his professional debut against Yuki Ishikawa at
K-1 World GP 2015 -60kg Championship Tournament on January 18, 2015. He won the fight by a first-round left hook knockout. Hiramoto faced Yuki Izuka at
K-1 World GP 2015 -55kg Championship Tournament on April 19, 2015. He won the fight by a first-round knockout. Hiramoto faced Yohei Noguchi at
K-1 World GP 2015 -70kg Championship Tournament on July 4, 2015. He won the fight by unanimous decision, with all three judges scoring the fight 30-25 in his favor. He scored two knockdowns in the first round: the first with a right straight, while the second was a standing knockdown due to a series of undefended strikes. Hiramoto faced the one-time
Krush lightweight title challenger
Minoru Kimura at
K-1 World GP 2015 Survival Wars on September 22, 2015. Kimura won the fight by unanimous decision, with scores of 30-27, 30-26 and 30-27. Hiramoto was knocked down with a left hook at the very end of the second round. After suffering his first professional loss, Hiramoto fought
Massaro Glunder at
K-1 World GP 2015 The Championship on November 21, 2015. Hiramoto lost the closely contested bout by majority decision, with scores of 29-29, 30-28 and 30-29.
Title fights Krush lightweight tournament Hiramoto participated in the 2016 Krush Lightweight tournament, held to fill the vacant title, following
Hideaki Yamazaki's move up to super lightweight. Hiramoto was scheduled to face Yoshiki Harada at Krush 62 on January 17, 2016 in the tournament quarterfinals. Hiramoto won the fight by a second-round knockout. He knocked Harada down with a right straight early in the second round, and quickly followed it up with a left hook. The referee decided to wave the fight off after the second knockdown. Hiramoto faced Taito in the tournament semifinals, held at Krush 64 on March 20, 2016. Taito advanced to the semifinals with a third-round knockout of Taro Hayasaka. Hiramoto won the fight by a dominant unanimous decision, with scores of 30-26, 30-26 and 30-25. He scored the single knockdown of the fight in the second round, dropping Taito with a left hook. Hiramoto faced
Daizo Sasaki in the tournament finals, held at Krush 66 on June 12, 2016. Sasaki earned his place in the finals with decision victories against Hisaki Higashimoto and Takayuki Minamino. Hiramoto lost the tournament final by majority decision, with scores of 29-28, 29-29 and 29-28.
K-1 lightweight tournament Hiramoto took part in the
2017 K-1 Lightweight World Grand Prix, held on February 25, 2017. He was scheduled to face the experienced Nak Muay
Brice Delval in the tournament quarterfinals. Hiramoto won the closely contested bout by majority decision, with scores of 30-28, 29-29 and 29-28. Hiramoto faced the WMPF World Super Lightweight champion
Gonnapar Weerasakreck in the tournament semifinals. Hiramoto knocked Gonnapar with a right straight at the 2:15 minute mark. He knocked Gonnapar down with a left hook at the 1:44 minute mark, after which the referee stopped the fight. Hiramoto faced the
Wu Lin Feng lightweight champion
Wei Rui in the tournament finals. Rui advanced to the finals with a stoppage victory against
Daizo Sasaki in the quarterfinals and a decision victory against
Cristian Spetcu in the semifinals. Rui won the bout by split decision, with scores of 30-28, 30-29 and 28-29.
Later K-1 career Hiramoto was scheduled to face Umar Paskhaev at
-1 World GP 2017 Super Welterweight Championship Tournament on June 18, 2017. He won the fight by unanimous decision. Hiramoto was scheduled to fight a rematch with
Daizo Sasaki at
K-1 World GP 2017 Heavyweight Championship Tournament on November 23, 2017. Sasaki won their first meeting, on June 12, 2016, by majority decision. Hiramoto won the rematch through by unanimous decision, with scores of 30-25, 30-26 and 30-26. Hiramoto knocked Sasaki down twice at the very end of the round, although he was unable to finish him. 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. He won the fight by a second-round knockout. Combat Press would later name his win against Kaew as their 2018 "Upset of the Year". He won the fight by a first-round technical knockout. Subsequently, he retired from kickboxing in order to pursue a career in professional mixed martial arts. until July 2020, when he transitioned to
mixed martial arts, and signed with
Rizin. ==Mixed martial arts career==