SO here is a thought, you know the tail of the Orochi and how it was decapitated  and killed by the Susanoo god of storms? Well what if ( what with it being a giant 8-headed demonic serpent ) it didn't die properly. What if what we are dealing with is an being born from one of the 8 decapitated heads an is working on gathering power to be fully resurrected to the Orochi again?