On June 25, 2011, Kubo won the tournament in the lightweight class. He was going to retire if he lost and visited his sponsors to tell them on the day before tournament. On February 17, 2012, Kubo defeated Charles François via second-round knockout to win the vacant ISKA World Light-Welterweight Championship in Tokyo, Japan. On June 8, 2012, At Krush 18 in Tokyo, Japan, Yuta faced who was talked to be his toughest challenge in Top Welterweight Abdellah Ezbiri. Prior to this fight Ezbiri revealed in an interview that he was shot in the face when he was a teenager. Despite his aggressive style Ezbiri seemed gun shy in the 1st round giving it to his opponent. Yuta dropped Ezbiri twice in the second, the 1st time with a right hook, the second with a spinning back fist but got up both times showing extreme toughness and heart and stayed on his feet in the 3rd even though Kubo is known for finishing his opponents quickly when he smells blood. Yuta Kubo won the fight by decision 3-0. He was expected to make his middleweight debut at ' on December 2, 2012 against an unnamed opponent but it fell through after the event was moved back to December 31 and combined with Dream 18. 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. However, Bennoui pulled out and was replaced by Roman Mailov. Mailov then sustained an injury in training as well, though, and lowly-ranked TaCa was brought in as Kubo's third opponent. He stopped TaCa with one of his signature body shots in round two. 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. A rematch with Abdellah Ezbiri then awaited him in the final. Kubo started the fight well but the tide started to turn in round two when Ezbiri began taking advantage of his injured leg to the point where he was having trouble standing. The bout was scored a unanimous draw after the regulation three rounds and so it went to a first extension round which was called a majority draw, much to the distaste of the crowd who booed the decision as they believed Ezbiri was dominant. Kubo rallied in the second extension round to take a unanimous decision, winning the tournament and the inaugural Krush 67 kg title. He established himself as the world's top 65 kg fighter by winning the eight-man tournament at ' on May 3, 2013. He KO'd Lim Chi-Bin with a second round body shot in the quarter-finals before taking unanimous decision victories over Gabriel Varga and Masaaki Noiri in the semis and final, respectively. 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. He was docked a point for excessive clinching in round three, allowing Noiri to take a wide unanimous decision. He lost to Mosab Amrani by unanimous decision at in Tokyo, Japan on December 21, 2013.
