1 Ryō 'Man'en Koban'

The Man'en koban was struck in direct response to a currency crisis triggered by the forced opening of Japanese ports under the 1858 Harris Treaty. Foreign traders, recognizing that gold was severely undervalued against silver in Japan relative to global exchange rates, began draining the country's gold reserves almost immediately. The Tokugawa shogunate's solution was to debase the koban dramatically — reducing gold content by roughly two-thirds compared to the preceding Ansei issue — bringing the internal gold-to-silver ratio closer to international parity.

The resulting coin is the lightest koban of the Edo period. Production ended with the Meiji Restoration in 1868.