The world's most versatile performer is floating like a six-metre-tall ghost above the ranks of the Japan Philharmonic Orchestra and two banks of chamber singers. Hatsune Miku's projected image trills a few lines from Isao Tomita's Symphony Ihatov, dancing delicately on top of the musicians, with a small kick here, a half-turn there, tilting her head from side to side. She pirouettes like a ballet dancer, looks up to the sky, and drifts off the ground, slowly dissolving into nothing - a creative twist to a performer leaving the stage.

Miku might seem like nothing more than a high-pitched singing cartoon, but she's the spearhead and symbol of a radical cultural phenomenon. Her anime-inspired avatar was invented to sell Yamaha's Vocaloid 2 voice synthesiser program, launched by Crypton Future Media (CFM) in 2007, which lets anyone construct a song from individual phonic units stored in a database. You type the words into the program along with their mood, pitch and length. "Anybody can be a producer of Hatsune Miku," explains CFM's marketing director Kanae Muraki.

Virtual stardom … "Vocaloid" pop star Hatsune Miku.

Miku's not the only Vocaloid character, but she's by far the most popular - her biggest hit, World Is Mine, has 15.6 million hits on YouTube. It's just one of an estimated 600,000 Miku works online, created by thousands of people.

The inspiration for this phenomenon struck when CFM relaxed copyright and offered a website, Piapro, where fans can remotely collaborate on songs and remixes. In doing so, it created a space for "Vocaloids" such as Miku, Kagamine Rin and Megurine Luka, around which the culture could grow. Next came the MikuMikuDance website, on which anyone can choreograph their own Miku pop videos (there are more than 267,000 on YouTube alone). And as well as the symphony described earlier, Miku has appeared in an entirely computer-generated opera, The End, with costumes drawn by fashion designer Marc Jacobs, which will next be performed in Paris in November.