A long time ago, long before Princess Luna had been banished to the moon, the two Princesses used to meet every evening at a window near the throne room, where Celestia used to set the sun and Luna raise the moon. But one day, Luna didn't come. The sun Princess looked for her a long time before finding her in one of the empty rooms of the castle.

That day is a day Princess Luna will never forget, not even long after her death...

~~~ Twilight Sparkle finds a book hidden deep in her library the day she was supposed to bring a visit to her teacher, the Princess. She brings it along, hoping to discover its secrets during her trip. What could that mysterious book named "To Luna" hide?