PLOT
A hundred years ago, the Demon Lord controlled the world and nobody could stop him. Later, the fish-like people sealed off the Demon Lord in order not to let him harm the world. The elders of the clan formed several battle arrays with the strength of the whole clan, and sacrificed themselves as guardian gods of arrays. Fearing that later generations would awaken the Demon Lord, the fish-like people built an island at the entrance of the arrays to guard him from generation to generation. Thousands of years later, the strength of the arrays gradually declined and the arrays were broken. Demons began to appear around the world. Several pieces of the remaining soul which escaped when the Demon Lord was sealed invaded the host constantly and the Demon Lord used them to help him break the arrays and re-emerge in the world.