When he first started his training at a young age, Umeno thought he would be World Champion easily, only to realize how good he would have to be.
Umeno was undefeated in his next eight fights, defeating Hiro, Okami and Hari Nagata by decision and Takaaki Sugano, Meechok Manopganchan, Yusuke Miho, Shinjin and Rajasaklek Sor Vorapin by (T)KO.
His 10–1 record earned him the chance to fight Yu Saenchaigym for the WPMF Japan Super Bantamweight title at REBELS 3.
[5] In his next fight, in September 2010, Umeno fought Egkarat for the WBC Muay Thai Japan Super Bantamweight title.
[6] Umeno fought his next three fights with the REBELS organization, defeating Yuya Kiyokawa and Suwannoi Acegym by unanimous decision, and Kaichon Sit Tamsap by a third round low kick knockout.
In November 2011, Genji fought Dekkamon Hiraigym for the WPMF World Super Featherweight title, and won by a first-round TKO.
Following these three wins, Umeno went on a 2–1 run, that nonetheless earned him the chance to fight Stephen Meleady for the WBC Muay Thai International Super Featherweight title.
[10] After drawing with the former Lumpini Stadium champion Singtongnoi Por.Telakun, he was scheduled to fight Jompichit Chuwattana for the WBC Muaythai World Super Featherweight title.
After defeating Rungrat Naratrikul at NO KICK,NO LIFE 2015, Umeno was scheduled to fight Phetmorakot Wor Sangprapai for the prestigious Lumpinee Stadium 130 lbs title.
[17][18] Following this title capture, Umeno won his next two fights, winning decision against Sirimongkol PKsaenchaimuaythaigym and Juan Mario Kaewsamrit.
[19] Umeno rebounded from this loss by defeating Suarek Rukkukamui and Inseetong Por.Phinaphat, before challenging Kulabdam Sor.Jor.Piek-U-Thai for the Lumpinee Stadium 135 lbs title at Rebels 54.
[22] After losing the tournament finals, Umeno fought Sila YZD for the Battle of Muay Thai lightweight title.
[26] Umeno faced Koji in the semifinal bout of a four-man tournament, held during the Rizin 29 – Osaka event.
[37] Umeno faced Yuto Saito at Rizin Landmark 6 on October 1, 2023, winning the bout via majority decision.