In the Japanese language, the gojūon (五十音, Japanese pronunciation: [ɡo(d)ʑɯꜜːoɴ], lit. "fifty sounds") is a traditional system ordering kana characters by their component phonemes, roughly analogous to alphabetical order. The "fifty" (gojū) in its name refers to the 5×10 grid in which the characters are displayed. Each kana, which may be a hiragana or katakana character, corresponds to one sound in Japanese. 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.

Wi is an obsolete Japanese kana, which is normally pronounced in current-day Japanese. The combination of a W-column kana letter with ゐ゙ in hiragana was introduced to represent in the 19th century and 20th century. It is presumed that 'ゐ' represented, and that 'ゐ' and 'い' represented distinct pronunciations before merging to sometime between the Kamakura and Taishō periods. Along with the kana for we, this kana was deemed obsolete in Japanese with the orthographic reforms of 1946, to be replaced by 'い/イ' in all contexts. It is now rare in everyday usage; in onomatopoeia and foreign words, the katakana form 'ウィ' (U-[small-i]) is used for the mora.