Kurt Rockhans, a kind-hearted fifteen-year-old boy, is abruptly expelled from the legendary adventuring party Flaming Dragon Fang for being useless in combat. An aptitude test confirms his fears, ranking his weapons, magic, and offensive skills at the lowest possible G rank. To make a living, Kurt turns to a temporary work agency and begins taking humble odd jobs such as repairing castle walls and mining for ore. It is in these everyday tasks that his hidden abilities begin to surface. Kurt displays astonishing talent in cooking, construction, mining, and crafting magical artifacts, demonstrating abilities that the kingdom classifies at the legendary SSS rank, a level of proficiency reserved for non-combat skills that few adventurers could ever hope to achieve. Kurt himself remains completely unaware of his greatness, believing his incredible feats to be entirely ordinary, a mindset rooted in the exceptionally high standards of the remote village where he was raised.

The story is set in a fantasy world where a formal aptitude ranking system from G to SSS governs the perceived potential of every individual. After being fired, Kurt is discovered by Yulishia, an adventurer formerly employed by the royal family. Stunned by the quality of Kurt's work, Yulishia realizes his extraordinary potential and becomes his partner, frequently acting as a buffer between Kurt's humble self-perception and the astonished reactions of those around him. Together, they encounter a colorful cast of characters, including the cursed noblewoman Liselotte, whose affliction is instantly lifted by Kurt's magically infused cooking, and the mysterious information broker known as Bandana, who subtly guides Kurt toward opportunities that benefit the kingdom. A court official, recognizing Kurt's value, instructs Yulishia to offer him a high-ranking position as an atelier meister. When she informs Kurt of his potential status, he politely brushes off the offer, refusing to see himself as above anyone else.

The narrative unfolds through a series of episodic adventures driven by Kurt's oblivious heroism. In one of the first major arcs, Kurt accepts work at an atelier harboring a dangerous secret. Later, Yulishia establishes a new atelier in a frontier town but keeps Kurt in the dark about his own role as its master. When the town is besieged by hordes of monsters summoned by a bishop and a demon lord to assassinate the princess Liselotte, Kurt single-handedly tunnels into the ruins from underground, saves a cursed girl named Marlefiss, and builds enchanted walls that help the defenders repel the invasion. In another notable arc, after helping a village resolve a water shortage, Kurt is given a mysterious egg that hatches into a three-year-old girl named Akuri, whom he begins raising as a father figure. Subsequent episodes involve Kurt and Yulishia defending a farm from a demon trying to kidnap Akuri, going on dates that are interrupted by thugs harassing a local meat bun shop, and using Akuri’s teleportation powers to uncover a margrave’s forbidden secret in a room where a demon is ultimately summoned. Throughout these events, Kurt continues to take as many odd jobs as possible, inadvertently transforming the lives of everyone he meets and becoming a pivotal figure in the kingdom’s protection, all while remaining completely unaware of his own greatness.