Kagamine Len (鏡音レン), sometimes referred to as Len Kagamine, is a humanoid persona voiced by the Japanese singing synthesizer application VOCALOID developed by Crypton Future Media. Kagamine Len is portrayed as a 14-year-old boy with blue eyes and blonde hair. His voice is sampled from Japanese voice actress Asami Shimoda. 
As Len has a mirror counterpart, Rin, Len's surname was derived from combining the words Kagami (鏡, mirror) and Ne (音, sound). While Rin's name is said to come from the English word "right", Len's voice is said to come from the English word "left". They are also said to be derived from the characters Ken and Rin from the manga Hokuto no Ken.
Kagamine Len has been a popular character to use for a variety of different songs. Some of these songs, which have been very sexually explicit, have become very popular.
List of popular songs
Gigantic O.T.N.: A song about how large Len's penis is 
Kurumi Ponchio: A song that makes euphemisms about "penis milk" 
The Runaway of Kagamine Len: A popular song featuring Len and his counterpart Rin. 
Both Len and his counterpart, Rin, have been featured on a variety of goods, including figurines, clothing, calendars, manicure sets, and smartphone applications.