In a world where magic has become prevalent, monsters roam the earth and gates to smaller worlds have opened up. Regular people and delvers coexist, with the latter having unlocked a "class" with abilities that they must cultivate themselves. Governments worldwide have collapsed, and humanity is divided into city-states that squabble over power.

Fifty years ago, the world almost ended, but a hero emerged and saved humanity. Now on his death bed, the hero is ready to come clean about how his journey to save the world really went down. The story switches between the present day, with the hero talking to a young historian, and the past story of his five-year journey to save the world.