Shinwa Densetsu No Eiyuu No Isekaitan (bestlightnovel-com)

Once upon a time, a boy was referred to as a “War Hero.” In another world called Aletia, the boy who had saved the Lost Kingdom, conquered their neighbouring countries, and led to the rise of a grand empire decided to throw everything away, returning to the modern era at the cost of his memories. As three years pa.s.s…