I Gained Enlightenment in Prison

(No harem, no routine, villain protagonist) The world has changed. How come all the ghosts from the underworld have escaped? Is there a prison in my brain? The prisoner Beelzebub? What the hell, isn't Beelzebub a demon? Is hell going to attack China? Then... Let's start the war! Evil appears and lurks in the human world. Who allows this? In this dazzling era, the fate of mankind is at stake. Will the crisis from a hundred years ago reappear? In the bloody storm, a man wearing a gray cloak stood at the top of human civilization. He looked at the demons all over the city and raised the corners of his mouth slightly: "In the end... Who is the devil?"