Beast essence system

What used to be myths and folklore changed 1500 years ago. Myth, folklore, the cursed, it's a lot of names that used to describe us but we are the altered. 1500 years ago gates to another world materialized on our planet unleashing mana and magic beast. Those magic beast killing everyone, modern weaponry couldn't stop them until the first altered found a beast essence. That was the turn of everything for us even though the magic beast were still stronger then use the beast essence gave us a fighting chance.