Nihon-shiki was invented by physicist
Aikitu Tanakadate in 1885, with the intention to replace the
Hepburn system of romanization. Tanakadate's intention was to replace the traditional
kanji and
kana system of writing Japanese completely by a romanized system, which he felt would make it easier for Japan to compete with Western countries. Since the system was created by a native Japanese speaker and was intended for Japanese people to use to write their own language, it is much more regular than Hepburn romanization, and unlike Hepburn's system, it makes no effort to make itself easier to pronounce for English-speakers.
Nihon-shiki was followed by
Kunrei-shiki, which was adopted in 1937, after a political debate over whether
Nihon-shiki or
Hepburn romanization should be used by the Japanese government.
Kunrei-shiki is nearly identical to
Nihon-shiki, but it merges syllable pairs / , / , / , / , / , / , / , / , and / , whose pronunciations in Modern Standard Japanese are now identical. For example, the word , rendered
kanadukai in
Nihon-shiki, is pronounced as
kanazukai in modern Japanese, and is romanized as such in
kunrei-shiki. The
International Organization for Standardization has standardized
kunrei-shiki, under ISO 3602. The
JSL system, which is intended for use instructing foreign students of Japanese, is also based on
Nihon-shiki. However,
some Japanese-speakers still distinguish di from zi and du from zu and so
Nihon-shiki spelling is not entirely obsolete.
Nihon-shiki is considered the most regular of the romanization systems for the Japanese language because it maintains a strict "one kana, two letters" form. Because it has unique forms corresponding to each of the respective pairs of
kana homophones listed above, it is the only formal system of romanization that can allow (almost) lossless ("round trip") mapping, but the standard does not mandate the precise spellings needed to distinguish , and . ==Romanization charts==