A 14 year old Vocaloid (a robot that sings and dances all electronically). He has yellow hair and dies periodically. It is actually a running gag that he dies in every music video.
His twin is Rin kagamine. They were both made from the same program, just set at different pitches.
Girl: Len Kagamine is soo cute!
Guy: But he dies every other day
Girl: he will live on in my heart
Guy: What about me?