Historically, some kokuji date back to very early Japanese writing, being found in the ''
Man'yōshū, (for example, iwashi'', meaning 'sardine', dates to the
Nara period during the 8th century,) while they have continued to be created as late as the late 19th century, when a number of characters were coined in the
Meiji era for new scientific concepts. For example, some characters were produced as regular compounds for some (but not all) SI units, such as ( 'meter' + 'thousand, kilo-') for kilometer, ( 'liter' + ) for kiloliter, and ( 'gram' + ) for kilogram. However, SI units in Japanese today are almost exclusively written using rōmaji or katakana such as or for kilometer, for kiloliter, and or for kilogram. In Japan, the kokuji category is strictly defined as characters whose
earliest appearance is in Japan. If a character appears earlier in the Chinese literature, it is not considered a kokuji even if the character was independently coined in Japan and unrelated to the Chinese character (meaning "not borrowed from Chinese"). In other words, kokuji are not simply characters that were made in Japan, but characters that were
first made in Japan. An illustrative example is . This spelling was created in Edo period Japan from the
ateji (phonetic kanji spelling) for the existing word
ankō by adding the radical to each character—the characters were "made in Japan". However, is not considered kokuji, as it is found in ancient Chinese texts as a corruption of (魚匽), '
catfish'. is considered kokuji, as it has not been found in any earlier Chinese text. Casual listings may be more inclusive, including characters such as . Another example is , which is sometimes not considered kokuji due to its earlier presence as a corruption of Chinese , "to press or extract juices". == Examples ==