User blog comment:B214/Question and Answers 6/@comment-30780538-20171125100202/@comment-3285616-20171125121334

Rias, Akeno, Asia, Koneko, Ravel, Zenovia, Irina, Rossweisse, Kuroka, Elmenhilde and Le Fay are certain as he has kids with them in DxD Ex.

Kunou is very likely, Abe is in love with Issei as well, but hasn't been mentioned for a long time. As for the other certainties, they'll fill up the rest of his peerage. Can't think of any other possibilities. Tiamat maybe.