"Goblin Slayer Side Story: Year One" is a prequel to the main "Goblin Slayer" series, delving into the origins of the titular character and his transformation into the relentless goblin hunter. The story begins with a young boy whose village is destroyed by goblins, leaving him as the sole survivor. Traumatized and consumed by vengeance, he adopts the name "Goblin Slayer" and dedicates his life to eradicating goblins. The narrative explores his early days as an adventurer, highlighting his initial struggles, lack of experience, and the harsh realities of the world he inhabits.

The manga portrays Goblin Slayer’s first encounters with the Adventurers Guild, where he is initially dismissed as a novice with an obsessive focus on goblins. Despite his inexperience, his unorthodox methods and single-minded determination set him apart. The story introduces key figures who influence his journey, including his mentor, a seasoned adventurer who teaches him the importance of preparation, strategy, and survival. Through these interactions, Goblin Slayer begins to refine his skills, developing the tactical prowess and ruthless efficiency that define him in the main series.

The plot also explores the broader world of adventurers, guilds, and the dangers they face. Goblin Slayer’s early missions are fraught with peril, showcasing the brutal and often underestimated threat posed by goblins. The manga emphasizes the grim reality of adventuring, contrasting the romanticized image of heroism with the harsh, often tragic outcomes of battles. As Goblin Slayer gains experience, his reputation grows, though he remains an enigmatic and solitary figure, driven solely by his mission.

Supporting characters play significant roles in shaping Goblin Slayer’s journey. Among them is Cow Girl, a childhood friend who provides emotional grounding and a connection to his past. Her presence serves as a reminder of the humanity he risks losing in his relentless pursuit of vengeance. Other adventurers, such as the Guild Girl and Spearman, offer glimpses into the camaraderie and challenges of guild life, though Goblin Slayer’s interactions with them remain minimal, reflecting his isolation.

The manga maintains a consistent focus on Goblin Slayer’s growth, both as a fighter and as an individual. His evolution from a traumatized survivor to a calculated, efficient hunter is central to the narrative. The story also explores the moral complexities of his mission, questioning the cost of his obsession and the impact it has on those around him. Through its exploration of his origins, "Goblin Slayer Side Story: Year One" provides a deeper understanding of the character and the world he inhabits, offering a compelling addition to the "Goblin Slayer" universe.