This Kagamine Len is from the song 'Imitator', which is about a Vocaloid!Len who is neither human nor android, but quite literally a Vocaloid program. Like real life! He slowly gained a heart, soul, emotions, and awareness by singing songs, and hopelessly sung in hopes that someone out there will realize that even without a body, he too is 'alive'. He was also apparently very lonely and despairing... and for good reason: He wished to become a human and leave the place he was trapped in, but of course there is no way for a computer program to do that!
Or was there?
Luckily for poor Len, one day he... like many before him... got pulled into the 'Dressing Room', a world where various worlds (all related to Vocaloids, their songs, and the UTAUs) merged. Somehow, in the process he got himself a body... something even he doesn't understand but certainly feels very very grateful for. Even if it's not human, it's close enough, and he's hardly alone in the DR being an android/robot.
Now the poor kid wanders around, trying to learn more about the world and himself. But the VDR isn't exactly the most sane or safe place to learn such things...