Mou Hitotsu no Piano no Mori: Totonou Oto

The spinoff manga centers on Satoshi Mukai, who once competed with Kai Ichinose in the Chopin Competition. Satoshi was so moved by Kai's performance, that he decides to pursue a career in the world of musical tuning. Satoshi needs to survive in an ordinary society while possessing a rare talent.

(Source: Anime News Network)