He reached the semifinals of the 2008 King's Cup, an amateur boxing tournament held in Thailand, before losing to Amnat Ruenroeng.
[1] Ioka joined Tokyo Agricultural University, hoping to represent his country in the 2008 Olympics but he would fall short on the qualifiers.
On December 31, 2012, Ioka beat undefeated José Alfredo Rodríguez for the vacant WBA (Regular) light-flyweight title at the Osaka Prefectural Gymnasium.
[12] On May 7, 2014, Ioka faced Thai IBF champion Amnat Ruenroeng at the Osaka Prefectural Gymnasium.
[14] On April 22, 2015, Ioka defeated WBA (Regular) champion Juan Carlos Reveco by majority decision (116–113, 115–113, 114–114).
[19] Ioka was knocked down for the first time in his career against 18 year old challenger and WBA interim champion Stamp Kiatniwat.
He was planning to defend on December 31 but his father stated that he would not be ready to do so, as he hadn't kept up with his training after getting married earlier in the year to Nana Tanimura.
[23] On New Year's Eve in 2018, Ioka fought three weight champion Donnie Nietes for the vacant WBO super-flyweight title.
In the tenth round, after leading on all three judges' scorecards, Ioka scored a TKO victory to become the first Japanese boxer in history to win a major title in four weight classes.
[26] Ioka made the second defense of his WBO title in an exciting fight against undefeated three weight champion and domestic foe Kosei Tanaka on New Year's Eve 2020 in Tokyo.
[31] Ioka was expected to face the IBF super flyweight champion Jerwin Ancajas in a title unification bout on December 31, 2021, at the Ota City General Gymnasium in Tokyo, Japan.
[32] The fight was officially postponed on December 3, as stricter COVID-19 measures imposed by the Japanese government prevented Ancajas from entering the country.
[33] Ioka was rescheduled to face the WBO Asia Pacific and OPBF super flyweight champion Ryoji Fukunaga instead, on the same date and at the same venue.
[38] On December 31, 2022, Ioka made his sixth super flyweight title defense in a unification bout with WBA champion Joshua Franco.
[42] A year later, on 31 December, 2023, Ioka made the first defense of his WBA super-flyweight title against Venezuelan boxer Josber "Avalancha" Perez.
Ioka justified his role as the vast betting favorite by knocking out Perez in the 7th round of their scheduled 12-round bout.
Ioka lost by unanimous decision to the IBF super-flyweight champion Fernando Martínez in a title unification bout on July 7, 2024.