In 1947 after two years as a Russian prisoner Yamaguchi returned to Japan. Upon his return Yamaguchi was shocked and heart broken by the condition of Japan after World War II. Not only the physical destruction but what he perceived as the spiritual decline as well. During the war many Goju schools had closed, there were a few that had remained open with no real leadership to guide them.

On the verge of suicide due to the state of his country and his art form, Yamaguchi experienced a revelation and discovered his purpose in life. He was to teach and spread the martial arts to the youth of his nation. He turned his attentions once more towards nature and religion. To aid in his goal of spreading martial arts Yamaguchi held a week long exhibition in Tokyo. This exhibition showcased the various traditional Japanese arts as well as various Chinese arts he learned while in China. Slowly, Yamaguchi began reconsolidating the Goju schools that had remained open through the war, while constantly opening new ones.

Yamaguchi was focused on the spread of martial arts and the betterment of himself physically, mentally and spiritually. He sought out Reverend Tadaki Yoshimura, Chief Reverend of Shin-shu Shinto, and eventually became a Shinto master as well. Yamaguchi also learned yoga from Tengai Noda, Japan's leading expert and yoga master at the time. Eventually Yamaguchi would meld these together with his Goju to form his personal system of Goju Shinto.

In 1963 there were two non-Asians training under Yamaguchi in Tokyo. One was Merv Oakley an Australian skilled in the art of Jujutsu. The other was Lou Angel an American who held a 2nd Dan in Goju as he had learned it from Peter Urban, another of Yamaguchi's students. Oakley earned his Shodan (1st black belt) in Goju at this time and when he went home he opened the very first Goju dojo in Australia. In 1970 Yamaguchi, at the invitation of Oakley, visited Australia and thus became the first Grandmaster to ever visit that country. At the tournament held in his honor, Yamaguchi amazed the crowd with his demonstration of the Goju Suparunpei kata.

The face of Goju ryu and martial arts in general would be amazingly different if not for the influence of Gogen Yamaguchi. Primarily due to his efforts Goju-ryu was formally registered and recognized by the Butoku-kai, the governing body for Japanese martial arts. This is the same organization that awarded Yamaguchi the title of Renshi (senior expert/5th dan) in 1940. In 1950 he founded the Zen Nippon (All Japan) Karate-do Goju-kai, a national organization in Japan. In 1951 Yamaguchi took enough time for himself to get his Judan (10th black belt) from Chojun Miyagi. All the karate dojos in Japan were united in 1964 under the Federation of All Japan Karate-do Organization (FAJKO), which is today known ass the Japan Karate Federation (JKF). While accomplishing all of this Yamaguchi was appointed as Shihan (master) of the karate division of the Kokusai Budo Renmei, the International Martial Arts Federation in Japan. This appointment came from the federation chairman, Prince Higashikuni of the Japanese Imperial Family. Another noteworthy Imperial contact occurred in 1968 when Emperor Hirohito presented Yamaguchi with the Ranju-Hosho (Blue Ribbon Medal) for his contribution to the martial arts.

Even in his late 60's Yamaguchi showed no signs of slowing in his mission to spread the martial arts. He founded and opened the Japan Karate-do College in Suginami, a suburb of Tokyo, Japan. This school served as Yamaguchi's home as well as the Goju-kai headquarters. In order to give students of the college a well rounded martial arts education the ground floor dojo level of the building taught classes in Goju and other styles. The second floor was a yoga-shinto center for the education and practice of those two arts. The top floor served as a dormitory with accommodations for about 12 students.

Yamaguchi accomplished much in his life; he was a lawyer, a military officer, a Shinto priest, martial arts master, husband and father. He breathed life back into the dying art of Goju after WW II, and introduced it to the world. Together he and his wife Midori Yamaguchi raised five children, three sons and two daughters; Norimi Gosei Yamaguchi, Kishio Gosen Yamaguchi, Hirofumi Goshi Yamaguchi, Wakako Gogyoku Yamaguchi and Makiko Yamaguchi. Gogen "The Cat" Yamaguchi passed away on May 20, 1989 having been one of the 20th century's most influential people in the martial arts.