The Perfect World of Kai (2007)

Amamiya Shu transfers to Moriwaki elementary filled with hope and ambition. But it doesn’t take long before he gets picked on by the class bullies, and gets involved in a dare to play the mysterious piano in the forest. Igniting his meeting with an equally enigmatic child that goes by the name of Ichinose Kai, who seems to be the only one capable getting sound out of the thought to be broken piano. [from AnimeNewsNetwork]