Now who is Kagamine Len?

Apparently a male counterpart of Kagamine Rin.

Purely a product of fanart, I presume? Sort of like what happens when you move the "gender" slider in the software a bit too far... though why doesn't Miku have a male counterpart then?

Len is the male voice that comes with Rin. Miku only had one because they weren't all buried under giant bags of money back then.

piespy said: Purely a product of fanart, I presume?

As VacBob mentioned, it's completely real. They only revealed him quite recently.