The world of Toukiden Woniuchi is set in a version of feudal Japan that has survived a catastrophic event known as the Awakening. This great disaster tore open the sky and split the earth, allowing monstrous demons known as Oni to invade the mortal realm. For over a thousand years, humanity has fought back against this ceaseless threat through the efforts of the Mononofu, powerful warriors who possess the skills and spiritual strength to hunt and purify the Oni.

The story takes place several years before the events of the first Toukiden game, serving as a direct prequel that explores an earlier era of this endless war. The central figure of this narrative is a young Mononofu named Sako, whose journey forms the core of the plot. As a member of the Slayers, Sako is tasked with defending the remaining human settlements and pushing back against the Oni hordes. The manga follows Sako and a group of fellow warriors as they struggle to survive against increasingly powerful demonic foes, all while the fragile peace of their age begins to crumble.

The narrative is structured into five planned installments, released serially over the course of five months. This serialized format allows the story to focus on the harsh realities of being a demon hunter in a pre-industrial world, where every victory is hard-won and the threat of annihilation is always present. While the main games focus on a later, specific crisis, Woniuchi delves into the backstory of that universe, showing the foundation upon which the later conflict is built. The plot explores the duties and sacrifices of the Mononofu, highlighting the constant vigilance required to keep humanity safe from the Oni that lurk beyond the borders of civilization.