10 Yen - Shōwa 23mm pattern, security edge

The postwar Japanese monetary reform of 1948 was driven partly by SCAP directives — Supreme Commander for the Allied Powers had substantial influence over fiscal policy during the Occupation — and the Mint experimented with multiple diameter and composition combinations before settling on the bronze 10 yen that wouldn't appear until 1951. This 23mm nickel pattern with security edge was one of several rejected proposals from that process. Nickel was ultimately set aside, likely due to ongoing material allocation pressures in the still-recovering industrial economy.