四格勇者

It's the year 952 on Cartland Calendar, Demon King Krotin and four demon lords lead the demon army to attack the Cartland Kingdom in the northern part of the central continent. When the war is at a stalemate, a brave man Jad Dove fights into the Demon Capital alone and finally defeats the four demon lords and kills Demon King Krotin. Jad thought this would be the end of the war between humans and demons, but troubles keep coming one after another, and he also discovers the secrets of the Cartland Kingdom.