Currency

Currency (通貨, Tsūka) is any item accumulated and used to make purchases.

Xostya Currency
In Xostya, four primary metals are utilized as the monetary standard and valued in increasing value: Copper, Silver, Gold, and Platinum. About 1/4 of the copper coins were made from brass. Platinum coins were rarely used with the exception of merchants and nobles.

In addition to that, there does exist financial institutions supported by the government. Trade between nations exists through numerous official and unofficial channels; platinum in particular is used in international trade.

If gold coins were too heavy to be used as payment, big transactions were typically made with gemstones and the like. Some countries used gemstones to make a type of extremely high-value currency called gem coins, or they made coins of mithril or adamantite, or “gold plaques” which had value beyond their weight.

Japanese World of 2125 Economy
If you converted the price of a copper coin from Xostya into Japanese Yen, its worth would be about 1000 yen. One gold coin is also equivalent to 100,000 yen.

Trivia

 * Three gold coins were enough to feed a normal family for a whole month in Xostya.
 * By Xostya standard, 30,000 gold coins was viewed as a craftsman's 300,000 days, 821 years worth of money.