As the Leviathans became the first major intelligent species, they began making groups in order to be able to consume everything much faster, and much easier.
One of the Leviathans, one that was called Yetra became a leader of a bigger community of hunting groups. Around the time the dusk wars were about to start, the Leviathans sought the planet of Regnum.
They gathered together in smaller groups and began eating everything in their path.
While this was happening, a storm was striking the land, and Yetra was stuck under a tree that had fell over them. Unable to move. And since they were far away from where the intelligent life species had made their homes, no-one saw them.

They drank the water that the rain gave, and managed to survive for quite a while, but they were absolutely famished.
Around the time when HooH
Ascended, she began eating the tree, desperate for life, and as she saw her kind killed by The equilibrium, she knew her only salvation was devouring the tree.
After eating the trunk of the tree and stripping it of its leaves, she soon started devouring absolutely everything, and by the time HooH had left to bestow equilibrium upon other worlds, Yetra eventually devoured all of HooHs' species.
Even after this she was still unsatisfied due to her extreme hunger and eventually, she managed to swallow Regnum whole. Elated by the taste, she grew to believe that the purpose of the world was to be eaten, and so, she ascended and became Oroboros, the unsatisfied devourer of worlds, and the second aeon to ever exist.