Jōdai Tokushu Kanazukai
Jōdai Tokushu Kanazukai (上代特殊仮名遣; lit. Special kana orthography of the early era) is an archaic kana orthography system used to write Old Japanese during the Nara period. Its primary feature is to distinguish between two groups of syllables that later merged.
The existence and meaning of this system is a critical point of scholarly debate in the study of the history of the Japanese language.