Once every hundred years, the cursed labyrinth known as the Abyss opens, spreading a deathly corruption across the land. A demon who loves death presides over this realm, plunging the world into despair. The royal family has inherited the power to seal the Abyss for generations, protecting the kingdom from its curse. But now, the king has vanished. Word arrives that he has been imprisoned deep within the Abyss by Helmuth, a great aberrant being who rules its innermost depths. The kingdom is enveloped in deep despair as everyone senses the end is near.

Amid this hopelessness, a lone man quietly arrives at the guild tavern. His name is Allen. To carve his own existence into the world and to resist the despair overflowing from the Abyss, he decides to challenge the depths of the labyrinth. This is a story of a new adventurer, spun within the very beginning of the Abyss.

The world is one of classic dungeon exploration, where adventurers must navigate treacherous traps and powerful monsters from a first-person perspective. The narrative focuses on this new protagonist, Allen, as he undertakes his perilous journey. The setting is a kingdom on the brink of collapse, slowly being consumed by death as its protector king remains captive.

The first volume of the manga establishes the central conflict of a seemingly futile resistance against overwhelming despair. Allen enters the Abyss not as a prophesied hero, but as an adventurer seeking to make his mark. The story follows his initial descent into the labyrinth, where he must confront the dangers that have already claimed the king and broken the spirit of the kingdom. This is not a tale of guaranteed victory, but of choosing to fight against inevitable doom. The overarching narrative follows Allen as he ventures deeper into the Abyss, encountering the lingering effects of the king's disappearance and the growing influence of the demonic forces that now threaten to consume everything.