Doin was a samurai of Tomobiki in the service of the Shimamura Clan in Kanazaki Province. He was a good but not talented fighter who found his vocation in administrative work as head of the Samuraidokoro board.
In 256 DR, however, the itinerant monk Jinchin started a revolt in Kanazaki, gathering an army of ronin, bandits, criminals, and sorcerers. All samurai sent to arrest him vanished without a trace. In 257 DR, Jinchin led his huge army against the Shimamura samurai and at Kiroshima, Jinchin's army, joined by many oni, bakemono, and other monstrous creatures, destroyed the samurai army led by Doin and Lord Shimamura. Doin was one of the few survivors. He was convinced by fellow survivors, the Wanderer and Kuang, to go back to defend the Shiramura castle, but was too late and he found the castle burning and his family killed.
So Doin decided to hide his identity and under the name "the Monkey", and started fighting Jinchin's rule. He gained two more companions; the spirit woman Onoye, and the korobokuru Okotampe. However, he soon realized that it was impossible to defeat Jinchin with martial skills and decided to learn the way of the shukenja. During that time, Doin mastered the shukenja powers and using those, finally defeated Jinchin. Afterward he opened a school for shukenja in his home village of Tomobiki, but often traveled the lands of Kozakura to fight evil with his inseparable friends Onoye, Okotampe, and the Wanderer.
Doin was a not very capable warrior but he was very cunning. He was very good mediating disputes. He was very able in the administrative work and used his administrative knowledge on the battlefield with success. After training as a shukenja, he found enlightenment.