Emperor Tenmu was the 40th Emperor of Japan, according to the traditional order of succession. He reigned from 673 until his death in 686.
Memorial Shinto shrine and mausoleum honoring Emperor Tenmu
The Nihon Shoki entry of April 15, 683 CE (Tenmu 12th year), mandates the use of copper coins instead of silver, suggesting that Japanese currency predates his reign. Excerpt of the 11th century edition.
Early Japanese currency: Fuhonsen coins (富本銭), found in Asukaike (飛鳥池), thought to have been minted during the reign of Emperor Tenmu, end of 7th century, copper and antimony. Currency Museum of the Bank of Japan.