In the beginning, Yggdrasil formed the Digital World and filled it with life, calling his creations "Digimon". For a time there was peace. But, as in many tales, evil rose up to conquer the world in the form of the Seven Great Demon Lords, led by Lucemon. Despite overwhelming odds Lucemon's brother, Seraphimon, defeated the Demon Lords, and banished them to Purgatory for their actions. Once again the Digital World was at peace, led by the Three Celestial Digimon-- Seraphimon, Ophanimon, and Cherubimon. Seeing their strength and wisdom, Yggdrasil left the Digital World in their hands and departed for another realm.
In the hundredth year of their reign, a terrible disease swept through the Digital World known as the "Falldown Virus". Once infected, Digimon were wild and violent, wishing only for destruction and war. And not even the Celestial Digimon were immune. During an attempt to quell the fighting Seraphimon was infected, and he infected his friend Cherubimon and his lover Ophanimon. Once infected the three turned on each other, and in one, final battle, killed each other.
For the longest time the Digital World was in ruin, its inhabitants fighting for even the most basic resources to survive. But from the chaos came the Olympos XII, twelve Digimon with the power to unite the people. The Digimon praised them as gods, forgetting Yggdrasil. But in the 500th year of the Olympos XII's rule, their creator returned. Enraged that his people had forgotten him, Yggdrasil came to Plutomon, Jupitermon and Neptunemon's younger brother. He convinced Plutomon that he could rule the Digital World, so long as he would allow Yggdrasil to be known as god once again.
A terrible civil war ravaged the Digital World, pitting the members of the Olympos XII against each other. Neptunemon, Ceresmon, Marsmon, Apollomon, Bacchusmon, and Merukimon joined Plutomon, while Dianamon, Junomon, Mervamon, Venusmon, and Vulcanusmon followed Jupitermon. In the end, however, Plutomon betrayed all of them, creating Titamon to wipe them out. What he did not know, however, was Titamon's loyalty to Yggdrasil. With the Olympos XII defeated, Titamon turned on Plutomon, and killed him.
In the aftermath, Yggdrasil helped restore the Digital World, and created ten Digimon to lead the different races, who came to be known as the Ten Legendary Warriors: AncientGreymon, leading the Dragon Digimon; AncientGarurumon, leading the Beast Digimon; AncientBeetlemon, leading the Insect Digimon; AncientKazemon, leading Bird Man and Fairy Digimon; AncientMegatheriummon, leading the Mammal and Icy Snow Digimon; AncientSphinxmon, leading the Legendary Beast and Demon Beast Digimon; AncientVolcamon, leading the Ore and Mineral Digimon; AncientTroiamon, leading the Plant Digimon; AncientMermaidmon, leading the Aquatic Digimon; and AncientWisemon, leading the Machine and Mutant Digimon. The Digital World prospered once more, with yearly competitions held between the different races to foster friendship and commerce.
During a competition, the unthinkable happened: Lucemon escaped from Purgatory, now stronger after killing and absorbing his fellow Demon Lords. His new form, Shadowlord Mode, gave him the power to easily defeat the Ten Legendary Warriors. In one final gambit nine of the Warriors gave their lives by being absorbed by AncientGreymon, who underwent Ancient Spirit Evolution and became Susanoomon. With the power of his living weapon, the ZERO-ARMS: Orochi, Susanoomon finally slew Lucemon before succumbing to his own injuries. Inspired by the courage displayed by the Legendary Warriors, a lone Digimon Warp Digivolved into Imperialdramon Paladin Mode, and founded the Royal Knights.
The thirteen knights, Alphamon, Omnimon, Craniamon; Gallantmon, Magnamon, Dynasmon; Crusadermon, UlforceVeedramon, Kentaurosmon; Leopardmon, Examon, Gankoomon, and Jesumon were tasked with protecting the Digital World from any and all threats. For two centuries the Royal Knights fulfilled the wish of their founder. But one day all thirteen just vanished. No battle, no trace of them. It was as if the knights had never existed. With their protectors gone, Digimon grew afraid. And so they isolated themselves according to their kind: Beast, Knight, Nature, Holy, and Dark. Fear gave way to distrust, distrust to hate. Before long, another war had started.
Saddened by the Digimon's misguided ways, Yggdrasil made a drastic decision to involve humans in the war. The first was summoned years ago, and groomed to the task. But others are needed, and Yggdrasil has decided that they are needed now.