4 Mon "Kan'eitsūhō Iron Alloy; reverse イ I

By 1866, the Tokugawa Shogunate was hemorrhaging silver and copper reserves to meet treaty obligations forced open by Western powers after 1854, prompting emergency iron coinage as a stopgap measure. The "Kan'eitsūhō" denomination had been in continuous nominal use since 1636, but these late iron issues bear almost no relationship — metallurgically or economically — to their copper predecessors. The reverse kana イ served as a mint or batch identifier, a practice adopted to manage accountability across the fragmented emergency production.

The Shogunate collapsed within two years of this issue.