The wave dash (波ダッシュ, nami dasshu?)—Unicode U+301C—is used for various purposes in Japanese. Note, however, that in practice the full-width tilde (全角チルダ, zenkaku chiruda?)—Unicode U+FF5E—is often used instead of the wave dash, because the Shift JIS code for the wave dash, 0x8160, which is supposed to be mapped to U+301C [1][2], is not mapped to U+301C but mapped to U+FF5E [3] in Code page 932—Microsoft's Code page for Japanese, a widely-used extension of Shift JIS. In other platforms such as Mac OS and Mac OS X, 0x8160 is correctly mapped to U+301C, but it is generally difficult, if not impossible, for computer users in Japan to type U+301C, especially in legacy, non-Unicode applications. Also, the wave dash glyph in JIS/Shift JIS [4] is almost identical to the Unicode reference glyph for U+FF5E [5], while the reference glyph for U+301C [6] is roughly its “mirrored” version. Nevertheless, the Japanese wave dash is still formally mapped to U+301C as of JIS X 0213. Those two code points have the identical or very similar glyph in several fonts, reducing the confusion and incompatibility.
In Japanese, the wave dash is also used to separate a title and a subtitle in the same line, as a colon is used in English.
When used in conversations via email or instant messenger it may be used as a sarcasm mark or, in East Asia, as an extension of the final syllable to produce the same effect as “whyyyyyy” with “why〜〜” (as mentioned above, Windows users would most probably type it as “why~~”: notice the difference between U+301C 〜 and U+FF5E ~). Used at the end of a word or sentence in text communications, it often denotes something said in a sing-song voice, or similar to the use in instant messengers and email, depending on context.