Take Hatsune Miku for example. She is the first commercially successful virtual JPop star who sings her own songs (a vocaloid). It was a product that was sure to be successful.
Crypton Future Media, the company that dreamed her up, licensed a vocaloid engine from Yamaha and released their first vocaloid in 2004. They soon realized that a voice is not enough. In 2007, they released Hatsune Miku as the first vocaloid with a persona.
Hatsune Miku is a "android diva in the near-future world where songs are lost". It was a marketing idea with legs.
Within months of her release major studios were lining up to produce Hatsune Miku tracks. Fans also got in the act with popular songs and videos released through Nico Nico Douga (a Japanese video sharing site).
Songs such as Black Rock Shooter, The World is Mine, Magnet and Spice! hit the charts. Soon Hatsune Miku was performing major concerts all over the world.