Career beginnings

Kasahara made his professional debut against Pako Lai at Shoot Boxing 2017 act.2 on April 8, 2017. He won the fight by technical knockout midway through the first round, as Lai dislocated his left arm.^[2]

A month later, Kasahara was booked to face Genki Takeno at Shoot Boxing 2017 Young Cesar in Hanayashiki act.2 on May 13, 2017.^[3] He won the fight by unanimous decision, with all three judges scoring the bout 29–28 in his favor.^[4]

Kasahara faced his second foreign opponent, Kim So Hu, at Shoot Boxing 2017 Young Cesar in Hanayashiki act.3 on August 6, 2017.^[5] He won the fight by a first-round technical knockout, forcing Kim's corner to throw in the towel near the end of the round.^[6]

Kasahara faced Shuto Sato at Shoot Boxing 2017 act.4 on September 16, 2017, five weeks after his victory against Hu. He won the fight by unanimous decision, with scores of 30–26, 30–27 and 30–27.^[7]

Kasahara faced the WMC Japan super flyweight champion Koki Yamada in a 54.5 kg catchweight bout at Shoot Boxing 2017 Young Cesar in Hanayashiki act.4 on October 14, 2017.^[8] He won the fight by unanimous decision, with scores of 30–26, 30–25 and 30–25. Kasahara scored a shoot point with a head and arm throw in the first-round, and badly staggered Yamada with a flurry of punches near the end of the last round.^[9]

Kasahara faced Ryu, in his sixth and final fight of the year, at Shoot Boxing 2017 Young Cesar in Hanayashiki act.5 on December 17, 2017. He won the fight by unanimous decision. Kasahara scored two shoot points, one in the first and one in the third round.^[10]

Kasahara faced Keito Naito at Shoot Boxing 2018 act.1 on February 10, 2018. He knocked Naito down with a flurry of punches, before knocking him out with a right hook at the 2:48 minute mark of the first round.^[11]

Kasahara faced Genki Takeno at Shoot Boxing 2018 act.2 on April 1, 2018. He won the fight by majority decision. Two of the judges scored the fight 30–29 and 30–28 for Kasahara, while the third judge scored it as an even 29–29 draw.^[12]

Shootboxing super bantamweight tournament

Kasahara faced the fourth ranked Shootboxing super bantamweight Ryota Naito at Shoot Boxing 2018 act.2 on June 10, 2018, in the quarterfinals of the Shootboxing tournament.^[13] He won the fight by unanimous decision, with two scorecards of 30–27 and one scorecard of 30–28.^[14]

Kasahara faced the second ranked Shootboxing super bantamweight Kyo Kawakami in the co-main event of Shoot Boxing 2018 act.4 on September 15, 2018.^[15] He won the semifinal bout of the tournament by a first-round knockout, stopping Kawakami at the very end of the first round.^[16]

His 10–0 undefeated streak earned Kasahara the #2 ranking in the division, as well as the right to face Seiki Ueyama in the finals of the Shootboxing super bantamweight tournament, with the vacant title on the line. The bout was booked as the co-main event of Shoot Boxing S-cup 65 kg World Tournament 2018 on November 18, 2018.^[17] Ueyama handed Kasahara his first professional loss, stopping him with a flurry of punches at the 0:56 minute mark of the third round.^[18]

Kasahara fought twice more at super bantamweight, before moving up to featherweight (-57.5 kg). He first stopped Shota Tezuka with a right hook in the first round at Shoot Boxing 2019 act.2 on April 27, 2019,^[19] which he followed up with a third-round technical knockout of Eisaku Ogasawara at Shoot Boxing 2019 act.3 on June 23, 2019.^[20]

Early featherweight career

After successfully rebounded from his first professional loss, Kasahara moved up to featherweight to face Ponchan Bravegym at Shoot Boxing 2019 act.4 on September 28, 2019.^[21] He won the fight by unanimous decision, with scores of 30–27, 29–28 and 30–28.^[22]

Kasahara faced Lertchai Aor.Saensuk at Shoot Boxing GROUND ZERO TOKYO 2019 on December 3, 2019.^[23] He won the fight by a third-round technical knockout, stopping Lertchai with a flurry of punches in the final minute of the last round.^[24]

Kasahara faced Kaito Sakaguchi at Shoot Boxing 2020 act.1 on February 15, 2020. He won the fight by majority decision, after two extension rounds were fought.^[25]

Kasahara vs. Nasukawa

On June 23, 2019, Kasahara was booked in the highest profile bout of his career up to that point, as it was announced that he would face the Rizin FF flyweight and RISE World featherweight champion Tenshin Nasukawa at the July 12, 2019 Rise on Abema event.^[26] The non-title bout was broadcast by Abema and was held in front of an empty arena, due to measures implemented to combat the COVID-19 pandemic.^[27] Kasahara lost the fight by a first-round stoppage, as he was knocked down three times by the midway point of the opening round, which resulted in a technical knockout victory for Nasukawa.^[28]

Shootboxing Japan Featherweight champion

Kasahara, who was at the time the top ranked Shootboxing featherweight, was booked to face the #4 ranked featherweight contender Shota Tezuka for the vacant title at Shoot Boxing 2020 act.2 on September 19, 2020.^[29] He won the fight by a fourth-round technical knockout. Both fighters traded knockdowns in the second round, while Kasahara scored the sole shoot point in the first round.^[30]

Kasahara faced Shogo Kuriaki in a non-title bout at Shoot Boxing 2021 act.2 on February 7, 2021.^[31] He won the fight by unanimous decision.^[32]

Kasahara faced Shuto Miyazaki in another non-title bout at Shoot Boxing 2021 act.2 on April 10, 2021. Miyazaki failed to make weight before the fight, coming in at 58 kg, 0.5 kg above the featherweight limit of 57.5 kg.^[33] Kasahara won the fight by unanimous decision.^[34]

Kasahara faced Pon SirilakGym at Shoot Boxing 2021 act.4 on September 4, 2021, in his final fight at featherweight. Despite a poor start to the fight, which saw him get knocked down with a left hook in the first round, Kasahara rallied to win the fight by a second-round technical knockout.^[35][36]