On 18 January 2023, it was revealed that Inoue had entered into negotiations with the unified super bantamweight world champion Stephen Fulton.[118] Fulton was ranked No. 1 by The Ring and TBRB. The fight was expected to take place at the Yokohama Arena in Yokohama, Japan, on 7 May 2023, and would have been broadcast by Lemino domestically and ESPN+ in the United States.[119] The fight was postponed on 21 March, as Inoue suffered a fist injury during training camp.[120] The bout was rescheduled for 25 July 2023, at the Ariake Arena in Tokyo, Japan.[121][122] Inoue won the fight by an eighth-round technical knockout. 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.[123] Inoue had out-landed his opponent 114 to 47 in total punches and 70 to 24 in power punches by that point.[124] He became only the second-ever Japanese fighter to win major titles in four weight classes, following Kazuto Ioka.[1]
