User blog comment:B214/High School DxD EX/@comment-177.142.214.134-20160116175608/@comment-3435913-20160116213849

The fight between Great Red and Trihexa happened, resulting in the near destruction of 666 that it became too weak to awaken ever again. Great Red was weakened too, but continued to swim the Dimenional Gap until Evil Gods from another world broke through. With Great Red so weak now, it's existence was wiped out with ease, allowing the Evil Gods to storm into the universe.

This resulted in the war of the Ex's future, where the mythologies fight against the other worlds evil gods and allies. Issei's future revolves throughout this war, serving as the mythologies champion, and a substitute guardian of the Dimensional Gap (with or without Ophis and/or Lilith).

Due to this, Issei is hardly around for his kids due to the fact the war is still on. (The kids say he's busy in order not to spoil too much of the future than necessary. Ix feels neglected because he's the most powerful of the descendants, but realises that Ise can never be reached due to Diablos Dragon being Infinite, so he he has no further way to ever surpass him).

The evil gods realise they can't win with Issei being around, so they try to work out a way to kill him off before DxD. The solution is going back in time to change the future. The other worldly gods can't travel because their appearance in the past would have been physically impossible, so Loki goes instead since he was the first evil God Ise ever encountered. And thus BorN's timeline is created.