In 1935, at age 18 he became the youngest ever godan (5th degree black belt) when he defeated eight consecutive opponents at Kodokan (headquarters for the worldwide judo community).

Kimura's remarkable success can in part be attributed to his fanatical training regimen, managed by his teacher, Tatsukuma Ushijima.

[3] Daily randori or sparring sessions at Tokyo Police and Kodokan dōjōs resulted in numerous opponents suffering from concussions and losing consciousness.

First, he trained what today is known as Shotokan Karate under its founder Gichin Funakoshi for two years, then switched to training Goju-Ryu Karate under So-Nei Chu (a pupil of Goju-Ryu founder Chojun Miyagi) and finally became an assistant instructor, along with Gogen Yamaguchi and Masutatsu Oyama in his dōjō (the latter also going to university together with him and aikido master Gozo Shioda[5]).

[citation needed] In 1949, after touring for Hawaii, Kimura and his troupe formed by judoka Toshio Yamaguchi and Yukio Kato went to Brazil after an invitation by the São Paulo Shimbun.

The bout between Gracie and Kimura took place again in the Maracanã Stadium, before an audience of 20,000 people, including president of Brazil Getúlio Vargas.

The expectation was such that, according to a source, Kimura had been warned by the Japanese embassy that he would not be welcomed back in Japan if he lost the match.

After a number of holds by the Japanese, including kesa-gatame, sankaku-jime and do-jime, the Brazilian looked unable to breathe under Kimura, but he persevered until he tried to switch position by pushing with his arm.

On December 8, 1963, while partying in a Tokyo nightclub, Rikidōzan was stabbed with a urine-soaked blade by gangster Katsushi Murata who belonged to the ninkyō dantai Sumiyoshi-ikka.

However, Japanese author Toshiya Masuda would release in 2011 the book Why Kimura Didn't Kill Rikidozan, in which this theory is dismissed.

Kimura went to Brazil again in 1959 to conduct his last professional wrestling tour, and he was challenged by Waldemar Santana to a "real" (not choreographed) submission match.

[16] The Gracie side proposed a grappling match followed by a rematch under vale tudo rules ten days later, with Kimura accepting both.

[16] Nonetheless, the judoka threw Santana with seoi nage, hane goshi and osoto gari, and finally applied his famous gyaku-ude-garami.

[16] Newspaper Correio da Manha described the match as a "cat and mouse affair", while Diario de Noite stated "Kimura won at will".

[16] Kimura tried to execute ippon seoi nage, but he slipped and fell to the ground, where Santana started striking him with punches and headbutts through his guard.

The competitors, both tired and bleeding, disengaged and returned to standing, where they continued exchanging strikes until the clock marked the end of the match.