Kagamine Len is a virtual singer. He advises Vivid BAD SQUAD in the Street Sekai, though he also appears in Wonderlands x Showtime area conversations by default. 

Kagamine Len (鏡音レン) appears in the real world as a Virtual Singer, but when young people have trouble understanding their true feelings, Len and his fellow Virtual Singers appear in another world called SEKAI to help them.