Sing a song of Len's (or Rin and Len's) that shows off your voice well. I'd be willing to cast a female voice in this role as long as it was low enough. 

CHARACTER DESCRIPTION: I...I almost feel like Len is the meme of the Vocaloid community, though that might be because of his songs--where, if you need a reminder, someone always dies. Nevertheless, he's pretty submissive at Rin, and a bit of a pervert sometimes, though what portion of that is teenage boy and his own personality is hard to tell. 

VOCAL DESCRIPTION: I'm looking for someone who can have a somewhat higher feminine voice (alto range, most likely), and I'm willing to cast female voices for this part of the project, as well as the voice sounds masculine enough.