Mixing with humans’ history, monsters’ world still separate with them, so please don’t compare about the historical fragments in the story with real history.
In the Qin dynasty (B.C. 221~B.C. 206), human once broke wars with monsters. As the victory of humans, someone said that the rest part of monsters had been hidden in their arcadia, so called as the peach blossom spring, but no one believes with exactly.
After this lengthy war, monsters entirely disappeared from the eye view of human. Until East Jin Dynasty (265-317), a fisherman strayed into arcadia.
As the time past, the resentment of monsters to humans gradually slaked, so they entertained this special