Opposite the Crack

In his previous life, his parents died in a fire, his legs were broken, and he froze to death in a rental house. Reborn as a poor boy in a border town, he didn't bring the system - only to find out later that the system was in the hands of his enemies. He has only one brain of knowledge. Modify the furnace, make guns, and guard the town, making the poor days warmer inch by inch. Until he saw a line of words from his past life on the captured weapon—— The enemy in his previous life who burned down his whole family is now a young prince with power over the entire country. The enemy is on the throne, he is in the mud. Don't be anxious, he will walk up step by step with fire.