1 Bu Gin Ansei

The Bu Gin series was minted in direct response to the forced opening of Japanese ports under the Harris Treaty of 1858, which created an immediate crisis: foreign merchants discovered they could exploit the official gold-to-silver exchange rate and drain Japan's gold reserves through arbitrage. The Shogunate debased the silver coinage to close the gap, and the Ansei Bu — named for the era — was the instrument of that adjustment. It circulated through the final convulsions of Tokugawa rule, surviving into the Meiji transition before being demonetized.

The .873 fineness reflects a deliberate reduction from earlier Bu coinage, a compromise the Shogunate's finance officials calculated would neutralize foreign arbitrage without triggering domestic panic.