を, in hiragana, or ヲ in katakana, is one of the Japanese kana, each of which represents one mora. The combination of a W-column kana letter with を゙ in hiragana was introduced to represent [vo] in the 19th century and 20th century.
Modern usage
In Japanese, this kana is used almost exclusively for a particle for both forms; therefore, the katakana form (ヲ) is rare in everyday language mostly seen in all-katakana text. A "wo" sound is usually represented as うぉ or ウォ instead.
Despite originally representing , the syllable is pronounced by almost all modern speakers. Singers may pronounce it with the [w], as may those attempting to emphasize the syllable for clarity. Apart from some literate speakers who have revived [wo] as a spelling pronunciation, though, this sound is extinct in the modern spoken language.
In Romaji, the kana is transliterated variably as or , with the former being faithful to standard pronunciation, but the latter avoiding confusion with お and オ. is transliterated as in Modified Hepburn and Kunrei and as in Traditional Hepburn and Nippon-shiki.
Katakana ヲ can sometimes be combined with a dakuten, ヺ, to represent a sound in foreign words; however, most IMEs lack a convenient way to do this. The combination ヴォ is used far more frequently to represent the /vo/ sound.
Hiragana を is still used in several Okinawan orthographies for the syllable ; in the Ryukyu University system it is , whereas お is . Katakana ヲ is used in Ainu for .