Chopin's Etude Opus 25 No. 5 or “Wrong Note” was a piece played by Kousei in the Maihou Piano Competition.
Nagi Aiza played this piece to Hiroko Seto, demonstrating her skill to be at a very high level. The speciality of this piece is in its choice of notes along with the harmonies by Chopin,the combination of which is supposed to conflict with one another. But Chopin, the genius who he is, manages to make even the Wrong notes seem Right. The etude fits very well with the situation portraying how Kaori's entry in Kousei's life made the wrong into the right.