The puzzle of the sacrificial second princess

Claire, the second princess of the Feitnam Empire who was said to be a failure. Under a peace treaty with the enemy country, the Kingdom of Balatonia, she was sent as a hostage and went there expecting to be killed, but what was waiting for her was a warm welcome as the fiancee of the Crown Prince. She was recognised as someone with extraordinary intellect, and the people of the kingdom were longing for her! Having finally found her place, she generously utilizes the knowledge she has accumulated so far in order to enrich the kingdom. She embarks on a reform of domestic affairs and the manufacture of paper.