If you don’t know Kagmine Rin and Len then you should check them out! They are the brother-sister tandem of the vocaloid family; that is if you know Miku Hatsune. 😉
Though created separately in 2007; Rin on November 8 and Len on December 3, they were both released on December 27, 2010 officially as a pair. Rin and Len soared high not just in Japan but all over the world.