Justin Bieber. Kanye West. Katy Perry. What do all U.S. pop stars have in common? They are all human. Over in Japan, though, that's not always the case. Hot on the heels of their robot diva HRP-4C comes the animated chanteuse Hatsune Miku. Originally a mascot for audio software, Hatsune has begun performing holographic concerts for teeming crowds.