Copper Zaishen Coins are reward trophies from you killing sporatically and earning your kung fu. These rewards can be traded to this chick named Tesla in the Great Temple of Balthazar and Embark Beach. You get the low end of special items or you can trade your coins for higher coins like Silver Zaishen Coins, which can in turn be traded for Gold Zaishen Coins. Go, earn your Kung Fu, young-ling!