Meiji and Taishō (1873–1924)

One sen coins along with twelve other denominations were adopted by the Meiji government in an act signed on June 27, 1871.^[3] This new coinage gave Japan a western style decimal system based on units of yen, which were broken down into subsidiary currency of sen, and rin.^[4][5] The first coins minted were trial strikes or pattern coins, which are dated 1869 (year 2 of Meiji) and 1870 (year 3). No coins were struck for circulation right away as the technology to mass produce the coins was poor at the time. Silver and gold coins were thus given priority as they were produced and distributed to the market before copper coinage could be carried out.^[6] One sen coins were eventually introduced on August 29, 1873 via government notification.^[4] Each coin was authorized to be struck in an alloy of copper, weighs 110 grains (7.13g), and has a 1.10 inch diameter (27.9mm).^[7][8] Obverse features on the first one sen design include a dragon with the date of reign, and "1 sen" written in English. Reverse features include the value "1 sen" (written in Kanji) centered inside a wreath design. The Chrysanthemum seal is located at the top of the coin flanked by the words "100 for one yen" in Kanji. These coins were legal tender only up to the amount of 1 yen which was fixed by government regulations.^[9]

Production continued for a few years before it was stopped as no coins are dated from year 11 or 12 (1878 and 1879). It is theorized that the aftermath of the Satsuma Rebellion could have left an impact.^[10] When production resumed in 1880 (year 13), the scales on the obverse dragon design were changed from a square to a V-shaped pattern.^[11] This slightly modified first one sen design continued to be minted until 1888 (year 21), when coinage was stopped due to mass production and a slight oversupply.^[10] As with several other denominations it's possible that non circulating one sen dragon coins were made again in 1892 (year 25) for display at the World's Columbian Exposition.^{[lower-alpha 1]} The Japanese government officially switched to the gold standard on October 1, 1897 and new coinage laws were adopted.^[14] Changes for the one sen coin included a reduction of copper content by 3%, while the weight and size of the coins were left the same as before.^[15] Both sides of the coin received a brand new design as some of the older elements were no longer viewed positively. The dragon on the obverse side in particular was removed due to the First Sino-Japanese War which lasted from 1894 to 1895.^{[11][16][lower-alpha 2]} A rice stalk wreath was chosen to replace the dragon, while the reverse side of the coin received a sunburst design.^[17]

One sen coins continued to be struck for circulation in the Meiji era until 1902 (year 35). While coins dated 1906 and 1909 (year 39 and 42) were struck, none were released for circulation.^[18][19][20] Although production resumed under Emperor Taishō in 1913, World War I broke out in the following year. This event brought Japan a booming economy which required an increase of small denomination coins. At the same time rising metal costs to produce one sen coins became an issue, and their large size had made them difficult to distribute.^[11][17][21] Pattern coins were made in 1915 and again in 1916 to test out a smaller design which debuted in the latter year. This new design features the paulownia coat of arms, is 23.03 mm in diameter, and weighs 3.75g.^[11][22] The paulownia design was controversial at the time and seen as a liberal democratic trend which was criticized by those in the right wing.^[21] One sen coins with this design continued to be produced until 1924 (year 13 of Taishō) without any additional changes.

Shōwa (1927–1953)

One sen coins were minted again during Emperor Shōwa's 2nd year of reign (1927) using the Taishō era paulownia design. Meanwhile, events around the world including the Great Depression were leading up to another world war. Japan was pushed into a militaristic regime by 1933, and started stockpiling nickel as war materials.^[23] The Second Sino-Japanese War broke out in 1937 and a National Mobilization Law was declared in the following year.^[24] This action suspended the coinage act of 1897 and allowed the Japanese government to issue temporary subsidiary coins without obtaining approval from the Imperial Diet.^[11][25] New brass coins featuring a crow design on the obverse replaced the old copper paulownia coins on June 1, 1938.^[21][26] Brass was chosen as the previous composition contained tin which was a military-important metal not produced in Japan.^[27] The "crow" design with waves on the obverse, and eight ridge mirrors on the reverse was made by combining submissions from a public offering.^[27] On November 29, 1938 the act was revised and one sen coins were struck in aluminum as copper was needed for munitions.^[11][28] The diameter of the one sen coin was reduced from 23 down to 17.6mm, while the weight dropped from 3.75 to 0.90 grams.^[29] Although the coins were now smaller and lighter, the crow and waves design did not change.^[30]

By using aluminum, one sen coins were produced in large amounts as the alloy is naturally soft, did not require annealing, and extended the life of the dies.^[30] The design of the one sen coin changed again in 1941, featuring Mount Fuji on the reverse representing Hakkō ichiu.^[31][32] The obverse side shows the character "ichi" or "one" representing the value of the coin. This feature was allegedly handwritten by Isao Kawada, who was the minister of finance at the time.^[31] The diameter of the coin was also reduced from 17.6 to 16mm while the weight dropped from 0.90 to 0.65 grams.^[29] In April 1943 the Japanese government announced plans to use tin in coinage as aluminum was needed for more aircraft.^[11][33] This shift did not happen right away as one sen coins had their aluminum content dropped from 0.65 to 0.55g that year.^[11] However, as World War II dragged on the amount of available aluminum was eventually depleted.^[11][34]

Tin and zinc replaced aluminum for one sen coins when they were issued in March 1944.^[33] The final design used for these coins features a chrysanthemum crest with value on the obverse, and inscriptions on the reverse. Although tin was not an ideal choice for money as the metal is heat-sensitive and soft, the Japanese government had no alternatives.^[34] Supplies of tin were available at the time from occupied Southeast Asia where the metal was abundantly produced.^[34] This remedy was temporary as one sen coins were forcefully discontinued in 1945 due to a depleted tin supply from naval blockades.^[35] A last ditch attempt was made by making one sen coins out of porcelain in the final months of the war. These were never officially issued and were destroyed^{[lower-alpha 3]} afterwards.^[11][34][35] One sen coins were officially demonetized at the end of 1953 when the Japanese government passed a law abolishing subsidiary coinage in favor of the yen.^[2] By this time, excessive post-war inflation had made them redundant as they were rarely seen in circulation.^[36]

Meiji

The following are circulation figures for one sen coins that were minted between the 6th, and 42nd year of Meiji's reign. The dates all begin with the Japanese symbol 明治 (Meiji), followed by the year of his reign the coin was minted. Each coin is read clockwise from right to left, so in the example used below "一十二" would read as "year 21" or 1888. Some of the mintages included cover more than one variety of a given coin.

• "Year" ← "Number representing year of reign" ← "Emperors name" (Ex: 年 ← 一十二 ← 治明 ← Top of coin facing self)

Taishō

The following are circulation figures for one sen coins that were minted between the 2nd and 13th year of Taishō's reign. The dates all begin with the Japanese symbol 大正 (Taishō), followed by the year of his reign the coin was minted. Each coin is read clockwise from right to left, so in the example used below "二十" would read as "year 12" or 1923.

• "Year" ← "Number representing year of reign" ← "Emperors name" (Ex: 年 ← 二十 ← 正大 ← Top of coin facing self)

Shōwa

The following are circulation figures for one sen coins that were minted between the , and year of Emperor Shōwa's reign. The dates all begin with the Japanese symbol 昭和 (Shōwa), followed by the year of his reign the coin was minted. Each coin is read clockwise from right to left, so in the example used below "二十" would read as "year 12" or 1937. Coin patterns that include examples struck on porcelain are not included here as they were never issued for circulation.

• "Year" ← "Number representing year of reign" ← "Emperors name" (Ex: 年 ← 二十 ← 和昭 ← Top of coin facing self)