In a world where "Gates" connect our reality to dungeons filled with monsters, certain humans called "Hunters" have awakened supernatural abilities to fight them. Sung Jinwoo is an E-Rank Hunter, notoriously known as "The Weakest Hunter of All Mankind." After nearly dying in a hidden "Double Dungeon," he is chosen by a mysterious program called the "System," which allows him alone to level up, complete quests, and grow stronger like a video game character. As he transforms from a weakling to a god-like Monarch of Shadows, he uncovers the truth behind the Gates and a cosmic war between ancient beings that threatens to erase humanity.