I was forced to make magic tools for my sister, who was favored by a prince who loved magic tools. Working at our family-run, exploitative magic tool shop, I was pushed to my limits with an overwhelming amount of chores. When I collapsed from exhaustion, I was rescued by the 'Ice Duke'. 'If you keep this up, you'll die someday.' 'If you want to run away from home, the easiest way is to become engaged to me.' Following the slightly S-like orders of the duke, I agreed to a fake engagement. Despite his intimidating appearance, the duke treats me as a 'legendary magic tool maker' and cherishes me, which has helped me regain my energy. I even want to stay in the duke's household forever. However, my sister, panicked by my disappearance, steals and announces a dangerous technology I was secretly developing. Due to my sister's mistake, my family's reputation is ruined. With my parents fleeing after defaulting on their debts, I take over the shop! The customers of the shop include my sister's ex-fiancé, the prince, a princess, and the daughter of the head of the knights? Before I knew it, my magic tools were receiving attention from all over the country. [Book and manga adaptation in progress]