User blog comment:B214/High School DxD EX/@comment-50.139.232.230-20151229193920/@comment-1359322-20151230000515

Technically BorN is caused by the UL and Loki that arrived from the future.

Original Timeline: The LN timeline. UL eventually travels back to the past which caused
 * Diverging Timelines: Where events of the past is changed, one of them is High School DxD BorN. So the children from the future travel back to the past in
 * High School DxD EX: to destroy the UL before they do any significant changes and to merge the diverging timelines into one again.

Simply put UL travel back to the past created multiple branching timeline, one being BorN, DxD EX is meant to change that the events in BorN never happened, or to be specific merges back to the LN timeline.