[1] Ishii faced Yoddoy Kaewsamrit for the WPMF World Flyweight championship in his next fight, at KODO 4 on February 24, 2019.
[3] Petchthailand and Ishii fought an immediate rematch at the August 9, 2019 True4U event, with the WBC Muay Thai World Super Flyweight title on the line.
[4] Ishii faced Nuapetch KelaSport in a non-title bout at the November 13, 2019 Suk Wan Kingthong event.
[5] Ishii was booked to face Hiroyuki for the Battle of Muay Thai Super Flyweight title at BOM WAVE 01 ~ Get Over The COVID-19 on June 28, 2020.
[6] Ishii faced Yuya Iwanami in a non-title bout at NO KICK NO LIFE ~Shin Shou~ Diamond FES on October 29, 2020.
He won his promotional debut by a second-round technical knockout, after he forced Iwanami's corner to throw in the towel.
[13] Ishii returned to Battle of Muaythai for his next fight, a non-title bout against Kojima Nor.Naksin at BOM WAVE 06 – Get Over The COVID-19 on November 7, 2021.
[15] Ishii faced Khun Namisan Shobukai at BOM WAVE 08 – Get Over The COVID-19 on April 24, 2022, in his final fight with the promotion before signing with K-1.
He was booked to make his promotional debut against Kazuki Fujita at K-1 World GP 2022 in Fukuoka on August 11, 2022.
[17] Ishii won the fight by a third-round knockout, flooring Fujita with a right straight at the 2:41 minute mark of the round.
[18] Ishii faced Detchphet Wor.Sangprapai for the vacant WBC MuayThai World Super Flyweight title at The Battle of Muay Thai "OUROBOROS" on September 23, 2022.
[25] Originally a unanimous decision loss for Ishii,[26] the bout was later changed to a technical draw due to the second round knockdown being against the rules as it followed an illegal kick catch.