Reborn as the Village's Only Man!

Officials come out to the village to take the men for the army and reassign the widows to other households. The only man in the village is a researcher from a modern institute who woke up one day in the Solara dynasty with no way back, and he puts himself between the officials and the women. There is a coarse salt mine on the village land, and he knows enough to refine it into fine salt, which is what first brings money in. The Solara army gets pinned down in the field and he builds a hot air balloon to help lift them out. Word of that reaches a woman travelling the country in plain clothes, who grants him the right to make and sell salt. Firewood runs short, so he presses poor grade coal into honeycomb briquettes to burn instead, and she hears about that too. Then a man named Shen Fang comes to the village with bandits behind him, and the researcher draws up a hunting gun and arms the villagers with it. The woman is there to see it and gives her name. She is the empress, she wants guns made for the court, and she offers him a post to do it.