Shinkyoku Soukai Polyphonica: Eternal White

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 Eternal White revolves around the new Dantist, Snow Drop, a maid who cherishes her Ojou-sama more than anything, and her Contracted Spirit, Blanca, who is also known as the famous Contra Bass, Eternal White.

(Source: Night Constellations)