"The Classic of Mountains and Seas" is not a collection of myths and legends, but an encrypted "Geography of the Lost World". The real existence of the strange beasts and divine realms recorded in it were separated from reality by the "boundary membrane" of the ancient powers. Every few hundred years, the boundary membrane will periodically weaken, requiring "boundary masters" with special bloodline to redraw and strengthen it. The protagonist is the last unawakened descendant of the current generation of cutters.
