In the Ainu language, the small katakana ゥ represents a diphthong, and is written as w in the Latin alphabet.

[citation needed] Both う and ウ originate, via man'yōgana, from the kanji 宇 (pronounced u and meaning space).

Scaled-down versions of the characters (ぅ, ゥ) are used to create new morae that do not exist in the Japanese language, such as トゥ (tu).

For example, in the phrase Tutankhamun's cartouche, the recent loan cartouche uses the new phonetic technique, but the older loan Tutankhamun uses ツ (tsu) as an approximation: The character う is also used, in its full-sized form, to lengthen "o" sounds.

The character ウ can take dakuten to form ヴ (vu), a sound foreign to the Japanese language and traditionally approximated by ブ (bu).