Soul_Caliber
I think that by completing the book of law and mixing elements from dxd and index world's and with the help of the god recorded in the Bible leo has understood the fundamental forces of the universe to a level that supposedly surpassed anyone in both worlds but he denied reality and made his own which led him to becoming a fallen angel , a unique existence that's instead of following the law of the world he makes his own laws and follow them and the world is forced to follow his will but it tries to deny it which lead to this chaos