Thor Regus is a young man from the Dolgaria Empire, a militaristic nation where combat skills are valued above all else. Because his only talent is alchemy, a non-combat art, he is dismissed by his family and society. His father, Duke Balga Regus, volunteers him to be sent as a living sacrifice to the territory of the Demon Lord, expecting him to be killed on arrival.

Upon entering the demon lands, Thor is surprised to find its inhabitants, including the Demon Lord Rukie Evergard, to be rational and peaceful. Instead of being executed, his passion for crafting is recognized. Furthermore, the dark mana of the region awakens his latent potential, evolving his simple alchemy into Creation Alchemy, a power that allows him to manipulate all six elemental attributes and replicate any item by reading its description or seeing an image.

Hired as the Demon Lord’s court alchemist, Thor discovers a mail-order catalog left behind by a hero from another world. Using his new abilities, he begins creating items based on the catalog’s exaggerated advertisements. These creations, ranging from household goods to powerful magical tools, consistently exceed all expectations and vastly outperform anything known in this world. This transforms the demon territory, improving the lives of its citizens and turning it into a civilized power.

Thor is soon joined by a growing group of allies. Mabel Refrain, a half-elf who becomes his devoted maid, and Agnis Fraisad, a girl of Ifrit lineage who struggles to control her volatile fire powers, both find their lives changed by Thor's inventions. As the Demon Lord and her subjects grow to trust him, Thor must also contend with the Empire that discarded him. When his father schemes to use him again, Thor rejects his family name and chooses to live freely in his new home, eventually facing threats like rampaging monsters and even the Empire's holy sword with his overpowered creations.