Gojūon

As depicted at the right using hiragana characters, the sequence begins with あ (a), い (i), う (u), え (e), お (o), then continues with か (ka), き (ki), く (ku), け (ke), こ (ko), and so on and so forth for a total of ten rows of five columns.

Ye persisted long enough for kana to be developed for it, but disappeared in Early Middle Japanese, having merged with e. Much later, with the spelling reforms after World War II, the kana for wi and we were replaced with i and e, the sounds they had merged with.

The kana for moraic n (hiragana ん) is not part of the grid, as it was introduced long after the gojūon ordering was devised.

The gojūon arrangement is thought to have been influenced by both the Siddham script used for writing Sanskrit and the Chinese fanqie system.

[1][2] The monk Kūkai introduced the Siddhaṃ script to Japan in 806 on his return from China.

Specifically, the consonants are ordered from the back to the front of the mouth (velar to labial).

Proto-Japanese is believed to have split into Old Japanese and the Ryukyuan languages in the Yamato period (250–710).

The earliest evidence was from 842, by the monk Ennin, writing in the Zaitōki that Sanskrit /p/ is more labial than Japanese.

[7] In contrast, the earliest example of the alternative iroha ordering is from the 1079 text Konkōmyō Saishōōkyō Ongi (金光明最勝王経音義).