User blog comment:Jopjopjop/Volume 19 Quotes / Spoilers/@comment-24468758-20141103215412/@comment-1359322-20141104164742

It's Agreas. And the credit won't go to Issei only, it'll go to the entire D×D team.

As for the peerage thing, like i previously said, Issei has other goals at the moment, so even if Issei receives a promotion now, he'll not form his harem immediately. Like what Okita advice Issei, make more goals and do it at a slow but reasonable pace.