User blog comment:Crimson and Darkness/Volume 25 discussion blog/@comment-3965848-20180420163959

Assuming the future of Ex is still canon, it said that Azazel named Issei and Akeno's child, either he leaves that dimension sooner or the rest find out they can contact him and the rest who are fighting Trihexa.

Or he simply leaves a message for them, knowing he wouldn't be around for this predestine moment.