In a world where hunters — human warriors who possess supernatural abilities — must battle deadly monsters to protect mankind from certain annihilation, a notoriously weak hunter named Sung Jinwoo finds himself in a seemingly endless struggle for survival. One day, after narrowly surviving an overwhelmingly powerful double dungeon that nearly wipes out his entire party, a mysterious program called the System chooses him as its sole player and in turn, gives him the unique ability to level up in strength. This is something no other hunter is able to do, as a hunter's abilities are set once they awaken. He also unlocks a deeper ability to turn anyone he kills into a loyal minion called a Shadow. Jinwoo then sets out on a journey as he fights against all kinds of enemies, both man and monster, to discover the secrets of the dungeons and the true source of his powers.