Short answers, pulled from the story.
The Japanese yen is the official currency of Japan and the third-most traded currency in the foreign exchange market, after the US dollar and the euro. It is also widely used as a third reserve currency.
The Meiji government officially adopted the yen as Japan's modern currency on the 27th of June 1871, under the New Currency Act. It was defined as 1.5 grams of gold or 24.26 grams of silver, divided decimally into 100 sen or 1,000 rin.
The spelling traces to the influence of James Curtis Hepburn's 1867 Japanese-English dictionary, the first full-scale dictionary of its kind, which spelled Japanese "e" sounds as "ye" following an earlier vocabulary by Walter Henry Medhurst. The spelling "yen" is believed to have first appeared in the dictionary's 1872 second edition and persisted even after Hepburn revised most "ye" spellings back to "e" in the 1886 third edition.
Japan's prolonged ultra-low interest rate policy, maintained to combat domestic deflation, created a large yield differential with countries such as the United States that raised rates sharply to fight inflation. This prompted investors to move out of yen and into higher-yielding currencies. By July 2024, the yen had fallen to above ¥161 per dollar, its lowest nominal effective exchange rate in 37.5 years.
The Plaza Accord was a 1985 agreement signed by finance officials from major nations acknowledging that the US dollar was overvalued and the yen undervalued. Following the accord, the yen rose from an average of ¥239 per dollar in 1985 to a peak of ¥128 in 1988, nearly doubling its value against the dollar.
Japanese coins record the year of the reigning emperor's reign rather than the Gregorian calendar year, reflecting the traditional system of imperial eras. A coin minted in 1980, for example, bears the inscription Showa 55, the 55th year of Emperor Showa's reign.