Fifty years ago, a massive tower swarming with countless monsters suddenly appeared on Earth. Humanity was trapped inside, their path to the outside world completely severed. The only way to escape is to awaken as a "Hunter" and reach the 100th floor at the very top of the tower.

Yushi, a boy born on the 1st floor, works harder than anyone else but remains the absolute "weakest" existence, unable to awaken his abilities. However, everything changes one day when he fuses with a forbidden monster known as the [Shadow] that had fled from the upper floors. This grants him an unprecedented and bizarre power that no human should possess.

But this power comes with a price—a hidden quest that completely contradicts the very purpose of a Hunter: [Fight alongside the monsters.]

To make matters worse, assassins sent by the Grand Nobles, who desire the power of the [Shadow] for themselves, mark Yushi as a target for extermination. Is he an enemy of humanity, or its next evolution? Caught between a conflicting mission and relentless pursuers, Yushi draws ever closer to the dark truth behind the tower...