Five years ago, dungeons suddenly appeared on Earth, transforming the world and giving rise to a new class of warriors known as explorers. Among these skilled adventurers was Yoichi Yashiro, a talented fighter who had been tackling dungeons since their inception and was expected to have a bright future. During an exploration, his team was attacked by an irregular creature known as a Trial Monster. To protect his teammates, Yoichi sacrificed the vision in one eye, leaving him permanently one-eyed and branded a failure by those around him who believed he could no longer fight effectively.

Despite being labeled a failure, Yoichi refuses to give up his life as an explorer. Rather than accepting his fate, he develops an entirely new fighting style that compensates for his lost combat power by utilizing various items and resources found within dungeons. This determination leads him down the path of becoming an Alchemy Swordsman, a unique class that combines swordplay with alchemical techniques. The story follows Yoichi as he fights to prove his worth, with the ultimate goal of achieving a rematch against the Trial Monster that took his eye.

The main protagonist is Yoichi Yashiro, a resilient and resourceful explorer who refuses to be defined by his injury. His character arc centers on transforming what others see as a weakness into a strength through sheer determination and innovation. The setting is a contemporary fantasy world where dungeons have become a regular part of life, creating a hierarchy of explorers who venture into these dangerous spaces for treasure, resources, and glory.

The central narrative arc follows Yoichi's journey from being cast aside as a failure to developing his unique alchemical swordsmanship. His story represents a counterattack from the bottom, as he uses his one-of-a-kind abilities to rise through the ranks and challenge the assumptions of those who wrote him off. The manga chronicles his adventures as he masters his new fighting style, gathers dungeon items for alchemical purposes, and works toward the rematch that will define his redemption.