1 Mon 'Kan'eitsūhō' NISUIEI, blank reverse

The Kan'ei Tsūhō series, introduced under the Tokugawa shogunate, became the backbone of Japanese copper coinage for over two centuries — an extraordinary run by any measure. This early issue, attributed to the Nisuiei mint period of 1626–1636, predates the proliferation of mint marks and reverse characters that would later allow specialists to attribute pieces to specific casting facilities across Japan. The blank reverse is not an anomaly but a deliberate feature of the earliest production, before the shogunate began using reverse markings to regulate and identify regional output.