Bonus Chapter Meeting Fondue
Complete the Master Instrument with all the sounds the seller asks you, and you will unlock this chapter.
Bonus Chapter Marie's Test
Find all the 18 scrapes of the Phantom Notes and bring them to the man standing in front of Raphael's house after the end of the game, and you'll unlock this chapter. The notes are divided in group of 5 in various screens, just tap around and if you see one note quickly tap on the screen to find the other ones.