Starting from a Scrap Gun 1: Seventy-Two Styles of the Solitary Gun

About three hundred years ago, a disaster known as the "Great Collapse" destroyed the civilization of the old era. There is a gap of hundreds of years in the historical records, and technology and magic (or collectively referred to as "source technology") are separated from each other. People in this world can only dig out old weapons from the ruins and worship them as gods.