The Chōonpu (長音符), which appears as a ー (a long dash shape) indicates the use of a long vowel sound in the preceding character. The Chōonpu appears most often in Katakana, and very rarely in Hiragana.

Examples of the Chōonpu are as follows –

ハー would be pronounced ‘haa’

ヒー would be pronounced ‘hii’

フー would be pronounced ‘fuu’

ヘー would be pronounced ‘hee’

ホー would be pronounced ‘hoo’

Notice how the ー drags out the sound of the preceding character. This is in contrast to the sokuon (small tsu – っ) which acts as a pause instead.