The story begins with the protagonist, a young orphan boy named Shuou, living a harsh life scavenging for food in the back alleys of a city. He discovers he possesses exceptional eyesight, able to track fast-moving insects invisible to others. This unique ability is revealed when he notices a trail of blood leading to a sewer, where he encounters a wounded woman named Amane. Amane, a skilled assassin known as the "Death God of the Scarletless," has been betrayed and is injured. Shuou, despite his fear, helps her, and Amane, recognizing his extraordinary vision, offers to train him. She reveals she is a successor to an ancient combat art and seeks to pass it on, proposing a contract: she will provide him with food, shelter, and training until he can stand on his own, in exchange for him becoming her disciple and eventually passing on the art. Shuou, seeing a path out of his miserable existence, accepts.
Twelve years later, Shuou has become a formidable warrior, trained by Amane in the dangerous Grey Forest, a place inhabited by fierce creatures called "Mad Beasts." He is preparing to leave Amane's tutelage to explore the world. He is given a leather eye patch by Amane to conceal the severe burn scar on his right eye, which has rendered it blind. Shuou ventures out of the Grey Forest and enters the Murakumo Kingdom, a prosperous nation built on mineral resources and weapon manufacturing. He arrives in the capital city, Murakumo, a place he remembers from his childhood as an orphan.
Seeking work to fund his travels, Shuou visits a Job Placement Guild. He learns about a dangerous "Vassal Candidate Selection Test" for the kingdom's army, which also serves as a graduation exam for students of the prestigious "Jewel Academy." Despite the high mortality rate, the test offers a substantial reward and the opportunity to gain valuable experience. Shuou, confident in his skills, accepts the challenge.
He is assigned to a small squad for the test, which includes the haughty noble girl Aise, the lethargic but surprisingly capable Shitori, the boisterous and strong Kumoari, and the peculiar frog-like creature Jiro. They are also joined by Borji, a former mercenary whom Shuou had rescued from a brutal attack by Mad Beasts. The test involves navigating a treacherous ancient path through the Grey Forest, with limited supplies and the constant threat of dangerous creatures.
The group faces numerous challenges, including navigating treacherous terrain, rationing their meager food supplies, and confronting powerful Mad Beasts. Shuou's exceptional combat skills and knowledge of the Grey Forest prove invaluable, as he leads the group through perilous encounters, including a terrifying battle against two powerful "Red Agates" and a massive "Ouji Spider." He demonstrates remarkable composure and strategic thinking, often saving his companions from certain death.
During their journey, Shuou learns more about the world's social hierarchy, particularly the distinction between "Mudstone" holders (commoners) and "Colored Stone" holders (nobles with magical abilities called "Crystal Arts"). He also learns about the kingdom's political structure, the powerful Marshal Gwen Vladou, and the mysterious nature of "Brilliant Stones," which grant immense power and longevity.
The group's journey is fraught with danger and personal growth. Aise, initially arrogant and dismissive of commoners, begins to respect Shuou's abilities and leadership. Shitori, initially withdrawn and unmotivated, shows glimpses of her latent power as a Crystal Master, particularly in a critical moment against the Mad Beasts. Kumoari and Jiro provide comic relief and unwavering loyalty. Borji, the rescued mercenary, expresses his gratitude and offers Shuou a precious ring to deliver to a woman in the capital, a testament to his newfound respect.
As they near the end of the test, the group faces their greatest challenge: a massive horde of Red Agates blocking their path. Shuou, realizing the danger, devises a plan to use the remaining food as a distraction and escape through a hidden path. He single-handedly defeats two formidable Mad Beasts, the Ouji Spider and the Sougai, showcasing his extraordinary combat prowess.
The group successfully completes the test, albeit with significant hardships and losses. They return to the capital, Murakumo, where they are rewarded and recognized for their achievements. Aise, deeply affected by Shuou's actions and the bonds formed during the test, defies her father's expectations and abandons a prestigious noble banquet to rejoin her companions, cherishing the newfound camaraderie. Shuou, having found a sense of belonging and purpose, continues his journey, his path now intertwined with those he has come to call friends.
