Around this time, Mas Oyama also met Eiji Yoshikawa, the author of the novel Musashi, which was based on the life and exploits of Miyamoto Musashi, Japan’s most famous Samurai warrior. Both the novel and the author helped to teach him the meaning of Bushido, the Way of the Warrior. That same year, Mas Oyama went to Mt. Minobu in Chiba Prefecture, where Musashi had developed his style of sword fighting. Mas Oyama thought that this would be an appropriate place to begin the rigorous training he had planned for himself. Accompanied by a student, he went into the wilderness there to train, with a friend bringing food supplies to them once a month. After six months of training, his student was unable to handle the solitude and secretly fled during the night, leaving Mas Oyama completely alone to continue his training. After fourteen months of training in the wilderness, his friend informed Mas Oyama that he could no longer provide the monthly supplies of food, and Mas Oyama had to return to civilization.

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A few months later, in 1947, Mas Oyama won the karate section of the first Japanese National Martial Arts Championships after World War II. However, still feeling empty for not having completed the three years of solitude, he decided to dedicate his life completely to karate. Once again Mas Oyama left civilization for the wilderness, this time going to Mt. Kiyozumi, also in Chiba Prefecture, which he chose for its spiritually uplifting environment. This time his training was fanatical – 12 hours a day, every day, with no rest days, standing under cold buffeting waterfalls, breaking river stones with his hands, using trees as makiwara (striking boards), jumping over rapidly growing flax plants hundreds of times each day. Each day also included a period of study of the ancients classics on the martial arts, Zen, and philosophy. After eighteen months of rigorous training, Mas Oyama returned to civilization fully confident in himself and able to take control of his life.

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In the 1950s, Mas Oyama began demonstrating his power and skill by fighting bulls. In all, he fought 52 bulls, three of which he killed instantly and 49 of whose horns he took off with shuto (knife hand) strikes. In 1952, Mas Oyama traveled throughout the United States for a year, demonstrating his karate live and on national television. During subsequent years, he took on all challengers, resulting in fights with 270 different people. He defeated the vast majority of his opponents with just one technique. A fight never lasted more than three minutes, and rarely lasted more than a few seconds. Mas Oyama’s fighting technique was based on the Samurai warriors principle of “Ichi geki hissatsu”, or “One strike, certain death”. If he got through to you, the fight was over. If he hit you, you broke – if you blocked his punch, your arm was broken or dislocated, if you didn’t block it, your rib was broken. Because of his strength and skill, he became known as “the Godhand”.