Kurt Rockhans, a fifteen-year-old boy with a kind heart but absolutely no talent for combat, is unceremoniously kicked out of the famous hero party known as the Flaming Dragon Fang. His former comrades view him as nothing more than a useless errand boy, a burden who only holds them back from greater glory. Desperate to make a living in a fantasy world where an adventurer's value is strictly measured by their combat rank, Kurt visits a local job agency. To his confusion, he discovers that while his fighting abilities are the lowest possible G-rank, his aptitude for everything else is off the charts, a legendary SSS-rank. This includes skills like mining, cooking, construction, crafting, and cleaning. Unaware of the true scale of his own talents, he simply accepts any odd job that comes his way, from hauling heavy sandbags to digging tunnels.

During a mining job, Kurt meets Yurisha, a beautiful and capable former royal operative who is searching for resources. Stunned by the speed and quality of his work, she quickly realizes he is no ordinary boy. Yurisha hires him on the spot, and together with her party, the Sakura Corps, they establish a base in a frontier town. It is here that Kurt unknowingly begins his role as the Atelier Master, a prestigious and highly respected national engineer. While he believes he is simply performing chores like building a mansion, cooking magical meals, and crafting tools, his actions have world-altering consequences. His construction projects are completed in days rather than weeks, his cooking can lift curses and provide massive status buffs, and his ability to purify magic crystals in minutes provides a decisive advantage in battle.

Kurt’s oblivious nature becomes a central point of comedy and intrigue as powerful figures take notice. He is tasked with protecting Lieselotte, the third princess of the kingdom, who is in hiding from assassins. With his signature rice porridge, Kurt effortlessly removes a deadly curse from her, earning her undying loyalty and affection. As the princess and other capable female adventurers like Yurisha and the magician Mimico gather around him, a chaotic found family forms. They build a life together, keeping the secret of Kurt’s real position from him while trying to thwart the political machinations targeting the princess. To further complicate matters, Kurt receives a mysterious egg that hatches into a young girl named Akuri, who immediately calls him "Papa".

The story unfolds through several notable narrative arcs. The initial banishment arc establishes the consequences of losing Kurt, as his former party rapidly falls apart without his support, their equipment degrading and their leader unable to stomach normal food. The frontier town defense arc sees a massive demonic assault aimed at killing Princess Lise, only to be thwarted by Kurt’s hastily constructed but magically fortified walls. A later arc involves a village with a water shortage, where Kurt digs a well and inadvertently discovers a dragon, leading to the acquisition of the egg that becomes Akuri. Finally, the conspiracy arc reveals a mastermind named Scripter, a servant of the Demon Lord, who is responsible for the curses and assassination plots. In the climax, the group battles a summoned demon lord, with Kurt saving the day through his non-combat skills, earning him the title of honorary knight even as he remains blissfully unaware of his own legendary status.