So, this idea comes from the "Season 6 Wishlist" thread on Broken Angel01's "Digital Connections" forum, and it's partly inspired by Arcaner's "Prelude to Destiny." So without further ado…
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War of Twilight

In the Digital World's beginnings, the Digimon were simple creatures. For the most part, they lived in peace, aside from the occasional territorial struggle among the animal and dinosaur types.

But as time passed, the Digimon became stronger, smarter, and took on new forms. As they were in the past, these new forms were inspired by the Myths and Legends of the Material World.

They took the shapes of humans, dragons, all sorts of monsters… but all fell into two classifications…Light and Dark.

The Dark. Creatures of the Deep Sea, of the Underground, of the Moon. They were the sea creatures, the cave dwellers, the Demons. They were led by the three rulers of Darkness… Daemon, Barbamon, and Dianamon.

The Light. Beings of Fire, of the Sky, of the Sun. They were the dragons, the birds, the Angels. Their rulers were Seraphimon, Apollomon, and ClavisAngemon.

The two co-existed peacefully for a time… before their individual ascensions, Daemon and Seraphimon had been best friends. Apollomon and Dianamon were twins. And there were none wiser than ClavisAngemon and Barbamon.

But then…a prophecy had been found in the Kingdom of Darkness. It spoke of a Great Force rising from the Land of Light to destroy the Darkness. It spoke of humans.

The Kingdom of Light found a similar prophecy, that spoke of humans from the Land of Darkness extinguishing the Light forever.

Daemon was the first to take action. He met with Seraphimon under the guise of a peace talk, and copied his data. With this data, he created his first General: ShadowSeraphimon.

Seraphimon, enraged at this betrayal, called on one of the Light's greatest heroes: Imperialdramon Paladin Mode. Imperialdramon formed the Royal Knights, and elite order dedicated to protecting the Light. Among its numbers were Gallantmon, Dynasmon, Crusadermon, Magnamon, AlforceVeedramon, Craniummon, Sleipmon, and Duftmon.

In the Land of Darkness, Daemon called upon more generals, his fellow Demon Lords. Beelzemon, Belphemon, Leviamon, Lilithmon. Lucemon, however, decided to remain neutral in the conflict. To make up for his loss, and the sheer numbers of the Royal Knights, ShadowSeraphimon was added to their ranks, along with ChaosGallantmon, BlackWarGreymon, Neptunemon, and MaloMyotismon.

And, as both sides gathered their forces, the first human appeared…