To be precise, 「ー」 is mostly only used to extend vowels when it wouldn't change what Japanese/Chinese word it's referring to. For instance, 「お」 can mean "honora

To be precise, 「ー」 is mostly only used to extend vowels when it wouldn't change what Japanese/Chinese word it's referring to. For instance, 「お」 can mean "honorable", but 「おう」 means "king" and 「おお」 means "large". If you wanted to convey that you're saying "honorable" but dragging it out, you'd write it like 「おー」 such as in 「おーにいーさん」 ("Brooooother"), so it wouldn't be confused with 「おう」 or 「おお」 even though it'd be pronounced the same way. You could think of it this way: if you wanted to convey that you were saying the word "god" but stretching it out, the Japanese solution would be to write it as "go–d" (since "good" would have it be confused with a different word). (This isn't the only way to convey that a long vowel in hiragana isn't semantic, though. It's also common to write the vowel in small font, such as 「あぁぁ」 or 「ねぇ」) You can also write things that are usually written in katakana in hiragana instead. This makes it look softer, and is similar to the idea of writing English without capitalizing words (such as at the beginning of sentences). In these cases, you'd still use ー as if you were using katakana, such as in the song title 「とらぶるめーかー」 ("Troublemaker", the opening theme song from the anime Himegoto).