1 Mon 'Kan'eitsūhō' NISUIEI, reverse 十三 JŪSAN

The Kan'ei Tsūhō series, launched by the Tokugawa shogunate in 1636, was Japan's first successful attempt at a nationally unified copper coinage, replacing a chaotic mix of imported Chinese cash and privately cast imitations that had flooded domestic markets for decades. Production was authorized across multiple mints simultaneously — Edo, Kyoto, Osaka, and others — which is precisely why reverse marks like 十三 exist: they were mint or furnace identifiers, not denominations.

The reverse numeral 十三 ("thirteen") is among the documented marks used to attribute pieces to specific casting sites, though assignment of individual marks to particular furnaces remains contested in the specialist literature.