[3][4] Nicknamed "The Monster", Inoue is known for his exceptional punching power, possessing a knockout-to-win percentage of 89.65%, with 91.66% in world title matches.

In 2010, he took the bronze medal in the Asian Youth Championships in Tehran, Iran, and won the Japanese Junior Selection Tournament.

He then participated in the AIBA Youth World Championships, but lost to Yosvany Veitía in the third preliminary round.

[16] However, he was eliminated in the third round by Yosvany Veitía in the 2011 World Amateur Boxing Championships at the Heydar Aliyev Sports and Exhibition Complex in Baku, Azerbaijan, and lost to Birzhan Zhakypov in the final at the 2012 Asian Boxing Olympic Qualification Tournament in Astana, Kazakhstan.

[21][22][20][23] On 5 January 2013, Inoue made a light work of Thai national champion Ngaoprajan Chuwatana, by scoring a first-round knockout.

With this victory, Inoue became the first Japanese champion in 23 years to win the title in just four fights, tying the record held by Joichiro Tatsuyoshi.

[6] On 5 September 2014, Inoue faced Samartlek Kokietgym (17–5, 5 KOs) at the Yoyogi National Gymnasium, winning every round on all scorecards.

[27] In November 2014, Inoue vacated his light flyweight title and moved up two weight classes to super flyweight to challenge two division champion and current WBO junior bantamweight title holder Omar Andrés Narváez.

[30] The referee waved off the fight in the second round, after Parrenas was dropped twice and he could not get up, giving Inoue a KO win.

Kokietgym and Inoue won the fight by KO at 3 minutes and 3 seconds of round 10, successfully defending his title for the third time.

González stipulated that the terms offered for an Inoue fight weren't good enough, and turned down the contract.

[40][41] Inoue's fifth defense of his WBO title came against Ricardo Rodríguez in May 2017 and he won the fight in the 3rd round following a flurry of punches.

[43][44] On 16 November, it was announced that Inoue would face Yan Boyeaux on 30 December, in a show televised by Fuji TV.

[58] IBF bantamweight champion Emmanuel Rodríguez defeated Jason Moloney via decision in October 2018, booking his place into the semi-final against Inoue.

Inoue dropped Rodríguez three times in quick succession before the fight was stopped at 1:20 of the second round.

[62] [63] Inoue was set to face Nonito Donaire in the World Boxing Super Series finals on 7 November 2019.

[65][66][67] Inoue faced future WBO bantamweight champion Jason Moloney on 31 October at the MGM Grand Conference Center in Las Vegas, Nevada.

[69] Inoue faced his IBF mandatory challenger and current IBO bantamweight champion Michael Dasmariñas on 19 June 2021 in Paradise, Nevada.

[70][71] He scored three knockdowns in the span of three rounds, each one with a left hook to the body of Dasmariñas, to win via third-round stoppage.

[72] It was announced on 21 October 2021 that Inoue would be defending his bantamweight world titles in a voluntary defense against IBF No.

[87][88] Inoue won the fight by an eleventh-round knockout, as he stopped Butler with repeated body shots at the 1:09-minute mark of the round.

[94] On 18 January 2023, it was revealed that Inoue had entered into negotiations with the undefeated unified super bantamweight world champion Stephen Fulton.

In the eighth round, he first knocked Fulton down with a left hook and forced referee Hector Afu to stop the contest with a flurry of unanswered punches soon thereafter.

Tapales was knocked down in the fourth round and again in the tenth, with the second knockdown rendering him unable to rise from the canvas in time to beat the count.

[121] On October 3, 2024, it was reported that Inoue would defend his undisputed super bantamweight title for the third time, against the undefeated IBF and WBO mandatory challenger Sam Goodman in Tokyo, Japan on December 24, 2024.

[122][123][124] On 13 December 2024, it was reported that Goodman suffered a serious cut on his eyelid during sparring and the fight has been moved to 24 January 2025.

[130] In February 2025, it was reported that Inoue would face Alan Picasso Romero on June 14, 2025 at T-Mobile Arena in Las Vegas.