Piano no Mori

is a manga written and illustrated by Makoto Isshiki. The series was adapted into a movie on 2007 by MadHouse. An anime television series adaptation produced by Gainax will premiere in April 2018, followed b a second season in January 2019.

Plot
A tranquil tale about two boys from very different upbringings. On one hand you have Kai, born as the son of a prostitute, who's been playing the abandoned piano in the forest near his home ever since he was young. And on the other you have Syuhei, practically breast-fed by the piano as the son of a family of prestigious pianists. Yet it is their common bond with the piano that eventually intertwines their paths in life.

Official

 * Official anime site

Other Sources

 * Wikipedia