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An UTAUloid. Ruko is the second attempted joke character made by the VIPPERS of 2channel, to trick people into thinking she is the third Vocaloid from Crypton. She is a hermaphrodite and is able to sing as a male or a female. Officially, she is mostly male, but fans commonly regard her as a female due to her appearance.
She is tall in stature, and has black hair in twintails with blue highlights. Her eyes have red and blue heterochromia, which reflects fluency in both Japanese and English. Ruko wears only one glove, on her right hand. Her outfit is a sleeveless dress shirt covered by a sleeveless dress coat, complete with detached sleeves and necktie; she wears low-cut pants which exposes a pair of black string underwear.
She is often drowsy, hence her name's phonetic reading of "Yoku neru ko". Her character items are a pillow and a cup of coffee.