The puzzle is story-related, but to solve it in less than six moves may not happen without a bit of practice. It is worth 3000 merit points, and isn't accessible once you've completed it.
*** Spoiler - click to reveal ***To finish within 6 moves or less, hit the following notes in order, read from left to right:
1. Hit the fifth note.
2. Follow that with a touch on the fourth note.
3. Proceed with the third note.
4. Near the end by touching the first note.
5. Finish it with the second note.