Kagamine Rin/Len (鏡音リン・レン, Kagamine Rin/Len) is the second installment of the Vocaloid Character Vocal Series. The developer says that their family name was from the developing code combining Kagami (鏡, mirror) and Ne (音, sound), i.e., they are the mirror reflections meaning Rin "right" and Len "left.", with the first syllables of their given names a pun on “Left” and “Right”. According to Vocaloid’s official blog, the package includes two voice banks: one for Rin and another for Len, both provided by the seiyū Asami Shimoda. Despite the double voice banks, the package still sells at the same price as Hatsune Miku. Their only cameo appearance in an anime is in (Zoku) Sayonara Zetsubō Sensei, where the two and Miku (and various other people and characters) try out to be the voice of Meru Otonashi.

On June 12, 2008, Crypton announced the updated edition, named "act2", will be released in early July 2008. Users who had bought the old version will get an expansion disc free of charge. On June 18, 2008, beta demonstration songs using the new version were released on the company's official blog.

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