User blog comment:B214/Volume 22 spoilers/@comment-173.185.123.104-20160909174547/@comment-9595671-20160909230612

Yeah, unless Angels made by the Brave Saints can somehow be added into a Devil's peerage within the next 30 years and Issei doesn't use up every spot by then, Irina's not gonna be in Issei's peerage.

Another reason it can't be Tiamat is because Ddraig says that she hates him for a reason we still don't completely know, only that Albion wasn't involved so it wasn't their fight... provided Albion doesn't reveal she hates him too in the future.