During the following months, Musashi Miyamoto briefly established a kenjutsu school, but no historical records indicate where in Japan it was located.
In 1614 and 1615, a war erupted between the Toyotomi and the Tokugawa families, this time with Tokugawa Ieyasu as the shogun. The Toyotomi family was perceived by Tokugawa Ieyasu as a threat to his rule. Miyamoto Musashi took part in warfare and siege one last time when he participated in both the winter and summer battles in Osaka.
Most scholars believe that, as in the previous war, Musashi fought on Toyotomi Hideyoshi's side, but the exact details of his role in the war are unclear. Some believe that he joined Tokugawa Ieyasu's army when the shogun besieged the castle of Osaka.
Later the same year, Musashi entered the service of Ogasawara Tadanao of the Harima Province as a construction supervisor. Musashi helped in the construction of Akashi Castle and helped organize the layout of the town of Himeji. During his stay, he taught martial arts, particularly kenjutsu and shuriken throwing, and he perfected his Enmei-ryu kenjutsu style. During this period of service, he also adopted a son named Mikinosuke.
After running his dojo successfully for a few years, Musashi's reputation started to grow even more and he began to be considered one of Japan's best swordsmen. When Honda Tadamasa, the lord of Himeji castle heard about him, he ordered Miyake Gunbei, his most skilled samurai, to go to Musashi's dojo and show him that he was not actually Japan's greatest swordsman. Musashi accepted the fight and left the choice of the weapon (either a real sword or a wooden sword) to his opponent.
Miyake's orders were to test Musashi's ability, not to kill him, so he decided to cut a piece of bamboo from the garden to use as a weapon. Meanwhile, Musashi wielded his bokuto. Seconds after they had faced off, Miyake Gunbei was defeated.
In 1622, when his adopted son Miyamoto Mikinosuke became a vassal to the Himeji fief, Musashi started to wander across Japan again, this time ending up in Edo in 1623. While in Edo, he became friends with Hayashi Razan, a Confucian scholar who happened to be one of the shogun's advisors.
With the help of Hayashi, Musashi applied to become a kenjutsu teacher for the Shogun, but his application was refused as the Shogun already had two teachers. Musashi started to travel again, leaving the capital in the direction of Yamagata City, where he adopted his second son, Miyamoto Iori.
In 1626 Miyamoto Musashi received a visit from his son, Miyamoto Mikinosuke, informing him that his lord has died and that, following the tradition called junshi, he would commit seppuku (ritual suicide), following his master in death.
For a short while in 1627, Miyamoto Musashi and his son Miyamoto Iori went to live in Ogura, and later entered the service of Lord Ogasawara Tadazane.
"Musashi wielded his bokuto. Seconds after they had
faced off, Miyake Gunbei was defeated."
At the end of the year, he and Iori began to travel again. It is unknown where exactly they went and for how long they travelled. They settled down in Kokura in 1634 to train and paint, staying in one of the houses of Hosokawa Tadatoshi, the Lord of Kumamoto Castle. Musashi's main rival, Sasaki Kojiro, was a retainer under Hosokawa.
In 1634 Lord Ogasawara organised a non-lethal duel between Miyamoto Musashi and a yari (spear) specialist named Takada Matabei. As expected, Musashi won.
In 1637 Musashi fought during the Christian Rebellion of Shimabara, one of the very few turbulent events that occurred during the peaceful Edo period under the Tokugawa shogunate. However, Musashi was injured early the battle by a rock that fell on his leg.
His son, Miyamoto Iori, served with distinction in putting down the Christian Rebellion and was named "Advisor to the Lord", a highly praised position.