Sheet music, thankfully, isn’t hidden away in chests or has to be purchased for crazy amounts of Gil, but a few do have some hidden requirements. Each new composition is found on a piano in the world and is free to snag once you sit down. Even if you don’t feel like playing right then and there, make sure you always at least grab the music to add to your collection so you don’t have to backtrack later and get it. There are eight in total to find, and some will only come later in the story, but none are missable once you open up fast travel back to previous areas. This is the natural order you can collect them.