It was invented by physicist Aikitsu Tanakadate (田中館 愛橘) in 1885,[1] with the intention to replace the Hepburn system of romanization.
For example, the word かなづかい, rendered kanadukai in Nihon-shiki, is pronounced as kanazukai in modern Japanese, and is romanized as such in Kunrei.
The JSL system, which is intended for use instructing foreign students of Japanese, is also based on Nihon-shiki.
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 ô 王/おう, ou 追う/おう and oo 大/おお.