Shinkyoku Sōkai Polyphonica (神曲奏界ポリフォニカ ), also known as simply Polyphonica, is an all-age Japanese visual novel created by Ocelot and first released on the PC on April 28, 2006. Aside from the game, multiple series of light novels have been created, and a manga adaptation started in March 2007. An anime adaptation started airing in Japan on April 3, 2007. Another anime adaption aired from April to June 2009, and was a prequel of the events in the first anime.
Plot: In the continent of Polyphonica, spirits materialize in the world, surviving on the music that is played by humans, and live together with them. While the spirits don't appear often, some spirits have enough power to materialize in human or animal forms and live together with humans.
Dantists, who play special music called "Commandia," are widely respected in this world. They are usually in contract with powerful spirits. The story of Shinkyoku Sōkai Polyphonica revolves around the new Dantist, Phoron Tatara, the spirit that he made contract with, Corticarte Apa Lagranges, and their friends, in their daily life and work.
In the anime, episode 1 to 10 explored the relationship between humans and spirits in the world of Polyphonica. This is shown either from Dantist like Phoron, or Direnn. The last two episodes focus on the Commandia that connects both kind of creatures.
(source: Wikipedia)