This, along with the publishing of a philosophical work entitled Seikyo Yoroku, caused him to be arrested the following year at the instigation of Hoshina Masayuki, daimyō of Aizu Domain.

Yamaga proclaimed his belief that the unadulterated truth could be found only in the ethical teachings of Confucius, and that subsequent developments within the Confucian tradition represented perversions of the original doctrine.

Soon after his expulsion from Edo, Yamaga moved to the Akō Domain in Harima Province in 1653, befriending Asano Nagatomo and becoming an important teacher of Confucianism and military science in the region.

Wilson wrote that Yamaga thought of the samurai as a "sort of Warrior-Sage" and focused his writings on the perfection of this "transcendent ideal", but "this direction of thinking ... was typical of the scholars of the Edo Period in its tendency toward speculation".

[5] An important theme running through Yamaga's life and works was a focus on the greatness of Japan, and this became one of the reasons his popularity and influence were to expand in the rising nationalistic culture of the mid-twentieth century.

For this reason, the boundless eternity of its gods and the endlessness of the reign of its sacred line, its splendid works of literature and glorious feats of arms, shall be as enduring as heaven and earth.