Piano no Mori follows Shuuhei Amamiya, a transfer student, and Kai Ichinose, a troublemaker from the town's rougher districts. After transferring to Moriwaki Elementary and mentioning his piano skills to the other children, Shuuhei soon becomes the target of bully Daigaku Kanehira. Daigaku challenges Shuuhei to locate and play a cursed piano in the forest, an encounter that introduces him to Kai, who asserts that he owns the instrument and is the only one capable of playing it. Fascinated, Shuuhei follows Kai to the concealed piano in the woods and listens to him perform a lovely medley. Having gained the respect of both Shuuhei and the school music teacher, Sousuke Ajino, Kai now begins formal piano lessons.