Shinkyoku Soukai Polyphonica: Cardinal Crimson

In a place called Polyphonica, humans and spirits live side by side. Young musicians create magical sounds with their music, which binds the spirits to them. A struggling student named Phoron accidentally summons a spirit he met in childhood but later forgot about. Phoron could use all the help he can get, but this feisty spirit may prove to be more than he can handle!

(Source: CMX)