Izumo Mythology

Izumo Mythology can refer to the collected myths of a group of people—their collection of stories they tell to explain nature, history, and customs or to the study of such myths. According to Kyoto Kasshu, It is a History of his ancestors and the God that created the Spirit Planet, Maxus and his/her counterparts, Raava and Vaatu.

Kyoto Kasshu Version
Once upon a time, there was a God that came to existence. A God that brings order and creation. God created created the Spirit Planet named Maxus. After defeating Vaatu during the Harmonic Convergence in 19,829 BG, Raava continuously battled Vaatu, keeping darkness under control and the world in balance.

Armada Gekko Version
At the peak of society, humanity created a complex machine system the Glory System (Known by all as the G System), an amazing technology which could create any machine so long as there were plans for it. However, tragedy struck soon after an apocalypse gripped Earth. Humanity began to rebuild society as best they could and called the apocalypse the "Great Fall".