[6] His winning streak was snapped by Kazuki Fukada at SHOOT BOXING BATTLE SUMMIT-GROUND ZERO TOKYO 2017 on November 22, 2017, who beat him by split decision, after an extra fourth round was fought.
[10] His 15–2 record earned Kasahara the chance to challenge the reigning Shootboxing Japan featherweight (-57.5 kg) champion Genki at Shoot Boxing 2018 act.4 on September 15, 2018.
[11] Kasahara faced Kohei "MOMOTARO" Kodera in a non-title bout at SHOOT BOXING S-Cup 65 kg World Tournament 2018 on November 18, 2018.
[16] Kasahara challenged the reigning Shootboxing Japan super featherweight (-60 kg) champion Kazuki Fukada at Shoot Boxing 2019 act.4 on September 29, 2019.
[18] Kasahara's three-fight winning streak was stopped by Yota Shigemori, who beat him by a fourth-round technical knockout at Shoot Boxing: Ground Zero 2019 on December 3, 2019.
[19] Kasahara was able to rebounded from the fourth loss of his professional career with a third-round technical knockout of Taisuke Maeguchi at Shoot Boxing 2020 act.1 on February 15, 2020.
[23] He won the fight by a second-round technical knockout, forcing Suarek's corner to throw in the towel at the 2:18 minute mark.
[26] Kasahara faced Yota Shigemori at Shoot Boxing 2021 Champion Carnival on December 26, 2021, in his fourth and final bout of the year.
[28] Kasahara challenged the Shootboxing Japan Lightweight (-62.5 kg) champion Renta Nishioka at Shoot Boxing 2022 act.2 on April 10, 2022.
[30] Kasahara faced the KNOCK OUT Black Lightweight champion Bazooka Koki at Shoot Boxing 2022 act.3 on June 26, 2022.
[39] Kasahara was expected to face Anurak Tded99 in a super lightweight (-65 kg) bout at SHOOT BOXING 2023 act.1 on February 12, 2023.
[40] Anurak withdrew from the bout on February 3, after suffering a cut, and was replaced by the 2021 Sports Authority of Thailand Fighter of the Year Lamnamoonlek Tded99.