4 Mon 'Kan'eitsūhō' 21 waves

The Kan'eitsūhō four-mon was introduced in 1768 under the Tanuma Okitsugu administration as part of a broader effort to address chronic copper shortages that had plagued the Tokugawa monetary system for decades. Increasing domestic demand and declining Ashio mine output had made the standard Kan'ei one-mon increasingly expensive to produce. The four-mon denomination allowed the bakufu to reduce per-unit copper content while expanding nominal money supply — a fiscal expedient that drew considerable merchant skepticism at introduction.

The 21-wave reverse variety is distinguished from the later 11-wave type by die count and production period, with DHJ cataloguing two distinct sub-varieties across the short 1768–1769 striking window.