In 2018, the first year of what came to be known as the Era of Great Mutation, the ubiquitous "vital energy" swept across the entire Earth.
Animals mutated at a rapid pace, becoming monstrous beasts out of myth, some even powerful enough to withstand modern weapons with their bare bodies. Humanity, which had dominated Earth for thousands of years, fell from its throne at the very top of the food chain for the first time.
At the same time, unusual humans began to emerge. Their skin and bones were as hard as iron, and the fastest among them could even outrun bullets and cleave mountains and rivers with a single sword strike!
