Kei, the illustrator for the Kagamine, was given the concept Crypton intended: their approximate ages, an image of mirror, and an image of androids. No other directions were given as Kei had already illustrated Miku before. Rin was the first one to be illustrated and Len was made to match her, just as Crypton instructed. Their legs were also designed to mimic speakers.
Another cute Rin cosplayer from Japan’s Winter Comiket 2010! I wish she had a Len with her! Thanks again to Fumiki for sending this in!