Armored Demon

A long time ago, an adventurer accidentally unlocked the seal of the Demon's Coffin while exploring the ruins. The demon inside escaped and wreaked havoc on the city and attacked humans. At that time, the entire earth was like a hell on earth, filled with helpless shouts and cries for help. At this time, an angel appeared. He helped mankind temporarily repel the devil, and built Noah's City on an island and built walls as the last refuge of mankind. At this point, mankind began the 400-year-long wall era. ..... Just when humans were about to forget about the fear they had from demons, a sudden wave of demons instantly destroyed all the confidence humans had accumulated. Facing the demonic tide released by the demons of the Seven Deadly Sins, what is the ultimate fate of mankind?