Once they were called to restore Luna's power and rescue another princess trapped in another castle. Now, Luna needs the Nightmare Knights to assemble once again to restore something else. As Celestia travels the world on her many adventures and thrill-seeking journeys, Luna realizes she is bored by retirement. In just a few months she has done all that Silver Shoals has to offer. And when she's done looking outward for an answer, she's left to look inward.
She needs music. She needs to show Equestria who Luna is, not who a princess is expected to be. She needs her team to restore what it meant to just be a pony like her. And to do that, there is one place she needs to start. To find herself, Luna needs to restore a love for her darkness.
(Optional readings, because not everyone reads the comics: Nightmare Knights Parts 1-5, MLP: FiM Comic Issue #67 & #68, MLP: Friends Forever Issue #37.)
Story Arcs Guide
Chapters 1-9: Beginnings | Chapters 10-15: The Nightmare Knights Find A Producer | Chapters 16-19: First Gig in Fillydelphia | Chapters 20-28: The Crystal Empire Arc | Chapters 32-39: The Cloudsdale Arc | Chapters 40-50: Mirror Arc |