Rei Kagene is the shadow version of Kagamine Len, with his family name composing of the Kanji "Kage" meaning "shadow". Rei wears long gray pants a black vest, and black sleeves. His hair is let down; only the back is shoulder length, while the front is short. Rei is intelligent, but with a gruff and hard-headed personality. He has a habit of saying ルイに触るな! ('Rui ni shokuru na! roughly translated as "Don't touch Rui!")

--from VOCALOID wiki