User blog comment:B214/High School DxD EX/@comment-90.214.228.73-20160201234354/@comment-1359322-20160207030218

Then let me ask you this, does the UL impact the current story arc or previous story arc at all? Does the kid appearing have any impact on Rizevim's action changing? No there's not, EX has no impact whatsoever on the main story, so what if it takes place in the main story? It's still related to the main story and doesn't have any impact on the main story, so yes EX doesn't stand in the main story.

"それはBD・DVDに付く特典小説でご確認くださいませ. 特典小説だからこそできた物語です. 時系列はあまり気にされないでください、あくまで特別編ですので."


 * It's a special novel attached to the BD & DVD, please be assured.
 * It's a story made possible because it's a special novel.
 * Don't worry about the timeline too much because it's only a special edition up to the end.

Source: http://ishibumi.exblog.jp/23319433/