Sawatari Takeru was suddenly teleported to a remote village in Isekai. He immediately shouted with joy, "Hyahaa! Isekai Teleportation! I'm the Yuusha!", then went to the nearest store, sold all his belonging and purchased an iron sword, then to the Boukensha Guild and took a Crazy Dog Subjugation Quest. He stormed out of the village and fought the dogs... and got pawned in return... easily. Just as he about to die, a female Boukensha saved him. She introduced him to a safer job as a laborer for farmer. The dream of being a Yuusha is over in day one. A week of work cleaning Cow dung, he discovered that japanese letters is considered sacred text in this world and being used in official documents. Thus he applied for job in local goverment office and made an assistant secretary. As he worked in the office, he tried to reproduce modern inventions in this world. He found that in the surrounding area there are resources to create Gunpowder. Thus, with the help of his superior he began developing explosives for mines, then musket and cannon. Eventually he started up a company with slave girls as employees and selling soap and crepes. At the same time, the kingdom was threatened by the rising activities of monsters and Takeru's superior suggested the capital to use their firearms to fight back, but the knights just laughed at them. To prove them wrong, Takeru raised a volunteer army from slaves and farmers to exterminate the threat.