Have you ever wondered about how the musical numbers on MLP:FiM feel to the ponies, both the participants and the observers? "Fugue State", a fanfic written by horizon, explores this, centering on Lyra and Bon Bon as they go through some tough times while the events of the S3 season finale, Magical Mystery Cure, play out in the background.
Almost from its beginning, this fanfic throws you right into the deep end. The story itself is not particularly complex, but the storytelling is warm and heartfelt; and the music and the songs, described in vivid splendor, are where the story shines beautifully. Care is taken to emphasize how the spontaneous musical numbers are nigh irresistible, drawing in even those ponies that are trying to resist them, and this is mirrored in the fanfic itself: even a reader trying to not be affected will surely find themselves overwhelmed by the power and beauty of the atmosphere that the inaudible music creates. Where a regular good story would just paint a picture in front of your mind's eye, this one also plays musical numbers for your mind's ear, and it does so skillfully and prodigally.
It's rightly tagged as a romance story, too; the events of Magical Mystery Cure, often merely alluded to, form the backdrop for Lyra's and Bon Bon's conflict, and then their rediscovery and reaffirmation of their love as learn more about each other. They get a happy ending, of course — the only thing that remains denied to them is a complete musical number of their own, but although I was hoping for one, I understand why the author chose to eschew it. It adds a tiny blemish to what would otherwise have been a perfect, flawless happy ending, but in doing so, it also adds a touch of realism and depth.
If you like the music of MLP:FiM, and if you like Bon Bon and Lyra, and fan works that portray them as a couple, then by all means, read this one.