Keian Era

The Keian era (1648–1652) fell roughly half a century after the founding of the Tokugawa shogunate, a time when peace was taking hold even as the bakufu's aggressive daimyo attainder policy (kaieki) had flooded Edo with masterless samurai — rōnin who retained the right to bear swords but had lost their stipends and social standing. In Keian 4 (1651), the military scholar Yui Shōsetsu and his co-conspirator Marubashi Chūya plotted to burn Edo Castle and overthrow the shogunate; the plot, known as the Keian Incident (or Yui Shōsetsu's Rebellion), was discovered before it could be carried out. The uprising was widely understood to be fueled by the resentment of the swelling rōnin population, who kept their sword-bearing status while losing everything else. In direct response, the shogunate relaxed its ban on last-minute (matsugo) adoptions by dying daimyo within the same year and encouraged domains to hire rōnin, effectively redesigning the very conditions under which a warrior's right to carry a sword could be preserved. The episode marks a pivotal turn from rule by martial force (budan seiji) toward rule by civil administration (bunji seiji), and stands in sword history as an emblem of the tension between a rōnin class that held the formal privilege of the blade without the means to use it, and the resentment that nearly erupted into an armed assault on the shogunate itself.