[4][5] In September 2016, Kubo was detained and arrested by the Tokyo Metropolitan Police Department on allegations of assault causing bodily harm raised by his then-wife.
After divorcing, the two reached an out-of-court settlement, which obliged Kubo to pay his wife an undisclosed amount in damages, but spared him from being prosecuted by the Public Prosecutors Office.
[6] Yuta Kubo was put practicing taekwondo at age of 8 with his younger brother, Kenji under a Zanichi Korean family friend.
[7] Kubo made his professional kickboxing debut on January 22, 2005, against Shinji Aseishi as a featherweight (-57.15 kg) at NJKF "Infinite Challenge I", as a high school student.
[11] His stoppage wins over the #9 ranked Shōkō on September 24, 2005,[12] and the #5 ranked Yoshiaki Takano on November 20, 2005,[13] as well as his unanimous decision triumph over Shōgo Kokubun on March 6, 2006,[14] earned him the right to face top-ranked Masato Ōkawa in an NJKF featherweight title eliminator, which was held at NJKF "Advance IV" on May 3, 2006.
[17] Kubo faced Nichau Sithaikeriangtor in a super featherweight (-60 kg) bout at the Rajadamnern Stadium on September 10, 2006.
[21] His opponent withdrew on the day of the fight and was replaced by Somdet Por.Pantie, with the contest being upgraded to a -90 kg catchweight bout as a result.
[22] Kubo faced the WMC Hong Kong Super Featherweight champion Daniel in a -58.5 kg catchweight bout at NJKF "Fighting Evolution II -Muay Thai Open-" on January 28, 2007.
[30] Kubo's 16-fight undefeated streak was snapped by Nuang Solia, who was able to overcome the Japanese fighter by unanimous decision at a "Removing Land Mines" charity event, held on November 21, 2007.
Kubo suffered the first knockdown of his professional career during this fight, as his opponent dropped him with a left hook in the fourth round.
[32][33] Kubo challenged the WMAF World Super featherweight champion Takashi "TURBO" Nagatsuka at MAJKF "Break Through - 3" on April 29, 2008.
[34] Kubo was expected to face Rashata at "NJKF Start of a New Legend IX" on July 27, 2008, but was forced to withdraw after being diagnosed with bladder stones.
[35] Kubo faced Yosuke Mizuochi in the reserve bout of the 2009 Krush Lightweight Grand Prix, held on November 2, 2009.
As the one of tournament finalists, Naoki Ishikawa, was forced to drop out of the contest due to a cut on his left eyelid, Kubo stepped in to face Masahiro Yamamoto in the Grand Prix finals.
[44] Kubo faced Yoshimichi Matsumoto in the semifinals and was able to make quick work of his opponent, stopping him with a question mark kick 81 seconds into the opening round.
[45] Kubo faced the WBC Muaythai Japan lightweight champion Tetsuya Yamato in the tournament finals.
[49] These two victories earned Kubo a place in the K-1 World MAX 2011 –63 kg Japan Tournament Final, which was held on June 25, 2011.
Kubo faced Kizaemon Saiga in the quarterfinals of the one-day tournament and was able to overcome him by a narrow majority decision, with scores of 30–29, 30–30 and 30–29.
[56] Kubo faced Nils Widlund in another -64 kg catchweight bout at Fight For Japan: Genki Desu Ka Omisoka 2011 on December 31, 2011.
[58] On February 17, 2012, at Krush 16, Kubo defeated Charles François via second-round knockout to win the vacant ISKA World Light-Welterweight (64.5 kg) Championship in Tokyo, Japan.
Kubo competed in the Krush Grand Prix 2013 ~67kg First Class Tournament~ on January 14, 2012 and was initially set to fight Houcine Bennoui in the quarter-finals.
In the semis, Kubo dropped Shintaro Matsukura with a first round punch to the body and cruised to a unanimous decision but not without taking significant damage to his lead leg.
Kubo rallied in the second extension round to take a unanimous decision, winning the tournament and the inaugural Krush 67 kg title.
Kubo knocked Lim down with a knee to the midsection in the clinch in the final seconds of the round, which left the Korean unable to rise from the canvas.
[74] Kubo overcame Gabriel Varga by unanimous decision in the tournament semifinals and faced Masaaki Noiri in the finals of the one-day contest.
[76][77][78] Kubo had his three year-spanning, seventeen fight win streak broken in his rubber match with Masaaki Noiri at Krush.32 in Nagoya, Japan on September 1, 2013, losing his Krush 67 kg title in the process.
[82] Kubo faced Raz Sarkisjan in the quarterfinals of the 2014 K-1 World Super Lightweight Grand Prix, held on November 3, 2014.
[89] Kubo faced Keita Makihira at K-1 World GP in Japan Featherweight Championship Tournament on November 2, 2016, in his return to the welterweight (-67.5 kg) division.
[99] Kubo captured the tournament title, as well as the inaugural K-1 World GP Welterweight (-67.5 kg) Championship with a unanimous decision victory over Mohan Dragon in the Grand Prix finals.
[108] Kubo was scheduled to make his mixed martial arts debut, as a featherweight, against Shinobu Ota at Rizin 30 on September 19, 2021.