Different World Brave Holy Crown Heroic Knight War

A delinquent boy, Nan Yundan, who just hangs around all day, accidentally comes across a book with a strange picture of a magic circle. He was transported to a different world that he didn't know. But he was one of the Holy Crown Knights who defeated the Demon King in this different world. He was the heir chosen by the swordsman spirit called one of the Crown Knights. In this way, the Holy Crown War started in this unknown different world.