The Emperor's Secret Mentor

Flynn Ford, with unactivated System, opens shop in Chang'an. Drought and locusts plague. He provides Li Shimin with pesticide and locust-eating methods. He enters imperial court, resolves animal husbandry crisis, develops firearms to repel Turk cavalry, and uses vaccine to eradicate smallpox. Li Shimin appoints him Grand Chancellor and Prince of Zhao. Thirty years later, Flynn Ford sees prosperous Great Tang. His System completes mission, and he disappears.