十数年前に異次元と現世界を結ぶ通路「ゲート」が現れた世界。ゲートの出現以降、「ハンター」と呼ばれる超常的な能力を持った覚醒者たちが出現し、ゲート内のダンジョンに潜むモンスターを倒して大きな対価を得ていた。
ハンターはその内なる魔力を測定することで能力や力量を測ることができ、それによってS級からE級にランク付けされ、ハンターたちを管理するハンター協会から適したダンジョン攻略が斡旋される。そして、その能力は一部例外を除き、一度覚醒すれば成長することはない。
In a world where hunters — human warriors who possess supernatural abilities — must battle deadly monsters to protect all mankind from certain annihilation, a notoriously weak hunter named Sung Jin-woo 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. 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. He soon discovers that he has been chosen to inherit the position of Shadow Monarch, essentially turning him into an immortal necromancer known as the “King of the Dead” who has absolute rule over the dead, created by a god while in the middle of the war between its two creations of light and dark, the Rulers and the Monarch. He is the only Monarch who fights to save humanity, as the other Monarchs, who are actually the leaders of all monsters, trying to kill him and wipe out the humans.