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Used as a plaintext fallback of ruby: encloses a regular or traditional pronunciation to kanji (sometimes other types of words, e.g. katakana in parentheses following an English word) that the readers may not necessarily know how to read.
Used as a plaintext fallback of ruby: encloses an invented reading or a pronunciation borrowed from another language, which follows usually but not necessarily a kanji word, to conveys the word's deeper or second meaning (see 義(ぎ)訓(くん) (gikun)).
(Internet slang, with no content inside) Used to censor vulgar, profane or sensitive words or characters. A formal way to censor words in Japanese is using × or ○ instead. Compare 自主規制 in Japanese and x in Latin alphabet.
(Internet slang) Added to the end of a message, with short text inside (the right parenthesis is optional), as a sort of tone indicator.
(Internet slang, by extension, with no content inside) Added to the end of a message to indicate a lighthearted or joking tone (the right parenthesis is optional),.
