The history of modern Japanese coins starts with the opening of the Osaka Mint on April 4, 1871 right next to the Yodo river. Funnily enough Japan had a mint before it even had a postal system or railway.
The mint was set up under the watchful eye of TW Kinder who traveled over from England to help managing the process. Foreign experts were involved in the mint right up to 1889, by which time all the required knowledge was transferred and the mint became 100% Japanese.
The Osaka mint got its initial equipment from the British government, taking equipment that was no longer needed in Hong Kong. The mint staff also started the manufacture of the specialized materials that was needed for the coin-making process such as coke, soda and sulphuric acid.
Since the mint was the first real modern industry in Japan it was at the forefront of the country's modernization. For example, the mint banned its employees from wearing swords to work, and demanded that they cut off their top-knot style of hair.
In terms of capacity the mint could strike around ten million coins per year, which increased to 400 million by the 1920s. In 1922 and 1923 Japan decided to replace the small notes that it had in circulation and the mint went into double circulation producing a phenomenal 800 million coins per year.
The mint went on to grow from strength to strength, and opened both a Tokyo (1879) and Hiroshima (1945) branch. With the advent of these branches mintmarks were introduced to coins that indicated where they were stuck. There was also a Kumamoto branch, but it just refined metals rather than actually strike coins.
The history of the mint is just one of the fascinating parts of the history of Japanese coins.