I was going through Arthur scenes for the fic when I came across when they call Mephisto to see the Gehena Gate... If they do not know he is Samael the King of Time, and believe he is some random high ranking time.space demon, why did they expect him to be able to close the Gehena Gate? It can only be opened by Satan, so, if they expected him to be able to close it, they must know he is of Satan's blood. Also he said "not even I can stop time forever" which sounds like he is saying "if I, being the King of Time, can't do it, nobody else can".