Japanese Yen

Rice was used as a unit of value for a long time, which was measured in koku (1 koku = 180 litres of rice). In the 8-9th centuries, coins were already in use, but not to a significant extent.
Between 1336 and 1870 the so-called “mon” was used as a currency, which was based on the Chinese character mon. There was a hole in the middle of the coins, because they were put in strings (which is preserved by the 5 and 50-yen coins).
In 1871 the Meiji-government introduced the Yen, which replaced the oval-shaped coins. This is where its name also comes from (Yen, in Japanese “en” means “round”).
Seeing that Japan mainly relies on exports rather than imports, it is the country’s interest to keep the Yen weak, because a permanently strong Yen would discourage foreign customers from buying Japanese products, and foreign companies operating in Japan would also relocate their site to another country.