User blog comment:B214/Volume 21 info & spoilers/@comment-98.64.244.161-20160402144627/@comment-27876048-20160402222825

It certainly explains why Issei has so much responsibilities in the future even though he isn't a maou he probabily has a positian of influence/power similar to that of Zekram Bael or maybe even Azazel (minus being a inventor)