[4] Takeru is considered by many to be a generational talent and one of the greatest kickboxers in the modern history of the sport, alongside his compatriot Tenshin Nasukawa.

[38] Advancing to the semifinals, Takeru faced the two-time Kyokushin karate world champion Yuzo Suzuki at Krush 27.

[46] Takeru was scheduled to fight a super-fight with the Krush Bantamweight champion Taiga Kawabe at K-1 World GP 2014 -65kg Championship Tournament.

During the sole round of this high paced bout, Takeru managed to knock his opponent down twice, with Otaki finally verbally submitting 89 seconds into the fight.

[51] His quarter final bout with Prilip started tentatively, before Takeru upped the pressure towards the end of the second round and scored a knockdown with a right overhand.

[56] Takeru was scheduled to make the first, and only, career defense of his Super Bantamweight title against Charles Bongiovanni at K-1 World GP 2015 The Championship on November 21, 2015.

[57] Biongiovanni had earned the right to challenge Takeru with a first-round knockout of Danial Williams in a title eliminator match, which was contested on September 22, 2015.

[66] After defeating Kaito Ozawa, Takeru vacated the K-1 super bantamweight title with the intention of participating in the upcoming K-1 Featherweight World Tournament, held on November 3, 2016.

The remaining quarterfinal pairings pitted Kaito Ozawa against Josh Tonna, Elias Mahmoudi against Ryuma Tobe and Yun Qi against Shota Kanbe.

[70] Takeru was scheduled to make his return to competition against Victor Saravia at K-1 World GP 2017 Super Bantamweight Championship Tournament.

[72] Takeru was afterwards scheduled to fight Buvaisar Paskhaev, in another non-title bout, at K-1 World GP 2017 Super Welterweight Championship Tournament.

[74] Takeru was scheduled to make his first and only featherweight title defense against Wang Junguang at K-1 World GP 2017 Welterweight Championship Tournament.

[83] Takeru was scheduled to fight the 2019 Rajadamnern Stadium featherweight champion Yodkitsada Yuthachonburi, in the main event of K-1 World GP 2019: K’FESTA 2.

Immediately after the fight restarted, Takeru pressured with a combination of right and left hooks, resulting in a knockout, with 19 seconds remaining in the round.

During a K-1 press conference, held at the Edmont Metropolitan Hotel on September 20, 2019, it was announced that Takeru would fight the former RISE Bantamweight and K-1 Featherweight champion Yuta Murakoshi at K-1 World GP 2019 Yokohamatsuri.

[91] Takeru was scheduled to fight the reigning Krush Super Featherweight champion Leona Pettas at K-1 World GP 2020 in Fukuoka.

[94] Prior to his title defense, Takeru fought an exhibition match with Kizaemon Saiga, which ended in a pre-determined draw.

[100] The fight started out evenly, with Pettas utilizing his reach advantage to score points from the outside, while Takeru attempted to cut off the ring and pressure.

K-1 Japan group producer, Mitsuru Miyata, demanded that Nasukawa sign an exclusive contract with K-1 to be able to make the fight happen.

Two days later, K-1's official YouTube channel uploaded the full fight video of Segawa and Paskhaev but a few hours later it was deleted and re-uploaded without Masato's comments.

On August 29, 2017 Rizin executive Nobuhiko Takada said on Twitter "Two of the biggest superstars of kickboxing, Takeru vs Tenshin Nasukawa should be made right now!

In an attempt to quash the cold war and influence K-1 and RISE to make the Segawa fight, Nasukawa made sure the show was being broadcast live so Rizin was not able to cut any of his comments.

[110] On March 16, 2018, RISE president Takashi Ito, former K-1 fighter Hiroya and his lawyer, accused K-1 Japan Group's exclusive contract, illegal based on the competition law.

[113] On April 1, 2022 the bout was confirmed to happen on June 19, 2022 at the Tokyo Dome, marking the return of a kickboxing headlined event to the venue for the first time since 2006.

[116] On May 31 it was revealed that Fuji TV had opted out of broadcasting the bout, due to allegations that RIZIN president Sakakibara was dealing with the yakuza.

[120] On June 27, 2022 K-1 held a press conference at which Takeru announced he was taking a break from competition in order to heal physically and mentally.

On the same day, Takeru announced over social media that he would also operate his knee during the next few weeks, to heal damage in the ACL and MCL ligaments.

[123] Takeru made his first post-surgery professional appearance on November 6, 2022, as he faced former teammate Koki in an exhibition bout at a GAINA promoted event in his native Yonago.

At the same press conference, it was furthermore revealed that Takeru had signed an exclusive contract with Abema and would earn around $750,000 per fight from the live TV streaming website.

[127] ONE Championship CEO Chatri Sityodtong announced of April 28, 2023, that Takeru had signed a contract with the promotion, although the exact details of it remained unclear.