Aaron is an explorer of the so‑called "Divine Corpse Labyrinth." After he learns only the beginner sword skill [Slash], his skill growth hits its limit, and he’s kicked out of his exploration party as a dead weight. Still unable to give up on his dream of being an explorer, Aaron makes a reckless decision: he continues delving the labyrinth alone, using nothing but Slash. Everyone laughs at how inefficient and suicidal this is.

Ten years after being expelled, however, Aaron is on the verge of reaching the realm of the strongest swordsmen using Slash alone. In the future, when a great calamity erupts in the labyrinth, a mysterious hero known as "Gokuken (Ultimate Sword)" will quell it with a single blade. While the whole city is searching for the identity of this legendary swordsman, Aaron—never imagining that he himself is that hero—draws his sword again today.