On the continent of Endiness, there exists a myth about the strange star that lingers invariably in the sky, day or night, unaffected by time, never moving: the Moon That Never Sets. Every 108 years, it would emit a red glow, and a herald known as the Moon Child would descend upon the Earth to "fill the world with holy bliss". However, scholars eventually noted that what actually transpires every cycle is the spawning of destruction and fear by the name of the Black Monster.
There are hardly any records on the Black Monster, as everything related to it has been reduced to ashes. History cites that it first appeared 11,000 years ago, a time span that coincides with the end of the Dragon Campaign. Various myths of the Black Monster and the Moon Child describe it as "a demon who rebels against and devours the gods, an evil plague that rejects peace in the world, the god that is the Moon That Never Sets".
The legend says the Moon Child revives the gods on earth and purifies the world. The Black Monster abhors, hates, and despises it, and kills the Moon Child. This sad karma is endless. This god stays forever in the sky, and the world is in never-ending chaos. Librarian Ute, Disc 3: Deningrad
According to sources of the Mille Seseau National Library, back during the ancient reign of the Winglies, even the gods bowed to Melbu Frahma and granted him ultimate power. The dictator abused that power to scorch the land; in response, the Dragoons freed the gods and put an end to the Winglies. From then on, the gods have been floating in the sky, looking over the world as the Moon That Never Sets.
As the party continues their journey and speaks with various knowledgeable people, they hear numerous stories that add their own spin to the myth. Even Lloyd, the man who serves as the group's antagonist for the biggest part of the game, falls victim to a warped version of the story that he presents to the party as truth: He throws three nations into chaos as he collects the three Divine Moon Objects, believing them to be the key to regenerate the world; together, they shall give birth to the last, the 108th species prepared by the creator Soa – the Moon Child, a god that leads Humans to utopia. According to Lloyd's source, the Winglies felt threatened in their status as the supreme species and thus sealed away the god, using signets that can be dissolved by the gem, the dagger and the mirror. In this version of the story, the Black Monster is a devil intent on stopping evolution, who kills the Moon Child over and over in self-preservation.
The truth is something none of them could even fathom, and it is not until the finale of disc 3 that it is revealed:
The actual last species to be born from the 108th fruit is the Virage Embryo, the God of Destruction – the true Virage that "creates a utopia" by purging the world. Winglies from 11,000 years ago discovered the fate that awaited them, so they sealed the fruit by separating the flesh and the soul of the god. The flesh became the Moon That Never Sets that glows in the sky, and the soul was captured in the Crystal Sphere kept by Melbu Frahma, its unlimited magic power enabling him to conquer all other species. (This Crystal Sphere is the "god" that the distorted sources of the Mille Seseau National Library speak of.)
The Crystal Sphere, however, was destroyed during the last battle of the Dragon Campaign, and the soul of the God of Destruction slipped away, capable of being born now. The released soul started to wander in search of its body, the Moon That Never Sets, so that it could fulfill its purpose as the last god. Every 108 years, it repeats its transmigration by possessing a human body that would head for the Moon That Never Sets: The Moon Child in Endiness' many myths is the soul of the God of Destruction, its promised "holy blessing" the destruction of the world that the creator Soa desires.
And yet, after 11,000 years, the world still stands – owing its existence to the one Dragoon who knew about that grim fate and has devoted more than just their life to the repeated killing of the Moon Children. That Dragoon is Rose.
As the sole surviving Dragoon after the end of the Dragon Campaign, Rose stopped her own time to continue protecting and fighting for the world – even as she goes down in history as the Black Monster and the people call her a demon. The reason the Black Monster eliminates everything that crosses its path is due to the special power of the Moon Child that turns everyone around it into servants of the God of Destruction.
Thus, every 108 years, the moon glows blood-red, a Moon Child is born, and the Black Monster appears to slaughter everyone who may have been exposed to it. Every 108 years, Rose kills a newborn child, and countless people along with it.