Twenty-one years after Sung Jinwoo, the Shadow Monarch, used the Cup of Reincarnation to reset the world and erase humanity's memories of the horrors of the gates, peace has reigned. Jinwoo and his wife, Cha Haein, live a quiet life, and their son, Sung Suho, has grown up as an ordinary high school student, his immense powers sealed by his father to grant him a normal childhood. However, this tranquility is broken when gates begin appearing once more, connected to dungeons teeming with monsters, and a new generation of Hunters awakens to fight them.

During a dungeon break on his college campus caused by a new type of monster called Mist Burn, Suho finds himself in mortal danger. In that moment of crisis, his latent lineage awakens, and he is granted access to the Player System, just like his father once was. Overwhelmed, Suho is saved at the last moment by the shadow ant king, Beru, who has traveled across dimensions on the orders of the Shadow Monarch to watch over his son. Beru explains the new, more profound threat: the Itarim, a race of gods from outer space who seek to fill the void left by the death of the Absolute Being. With Jinwoo absent, preoccupied with holding back these cosmic entities in a distant realm, the defense of Earth falls to his son.

The narrative follows Sung Suho as he navigates his newfound power. Unlike his father, who started as the famously weak E-rank hunter, Suho begins his journey with a prodigious, if unrefined, strength that quickly surpasses S-rank hunters. He is forced to level up, not just in power, but in wisdom and control. Early on, he is designated as an E-rank by official tests, leading to him being treated as an Almighty Janitor, assigned to low-level mining teams while secretly being far more powerful. The story recontextualizes Jinwoo's ultimate sacrifice, suggesting his efforts to shouldering humanity's burden alone were not entirely successful, as the conflict with the Absolute Beings and the inevitability of the gates has resurfaced.

As Suho grows, he does not simply inherit the title of Shadow Monarch; the system guides him toward forging his own unique path and identity. He gathers a diverse group of allies, including the spirits of fallen Monarchs like Rakan of the Fangs, Sila of the Frost, and Querensha of the Plague, who serve as both mentors and powerful combat assets. Other key characters include Lee Minsung, an actor whose jealousy and ambition lead him to become a major human antagonist enabling the Itarim's goals, as well as veteran hunters like Baek Yunho and Liu Zhigang who step into more prominent roles supporting the new protagonist.

The major narrative arcs focus on Suho coming to terms with his father's legendary legacy, learning to master his abilities by conquering shadow dungeons, and uncovering the nature of the Itarim's plan to conquer Earth by manipulating human worship and creating chaos. The conflict quickly escalates from monster hunts to an interdimensional war, pushing Suho to explore the deeper mechanics of the Player System and his own unique powers. In the final act, Suho transcends his initial potential, ascending to the position of Monarch of Transcendence and becoming the Guardian of the World Tree. He leads his coalition of hunters and reformed monarchs to a final victory against the Itarim, restoring balance to the planet and allowing for an emotional reunion with his parents, thus securing a new legacy for the next generation.