User blog comment:B214/Volume 23 discussion blog/@comment-76.175.162.45-20170404042611/@comment-31137559-20170404231007

But then Kurenai told him that what happened to Sirzechs wasn't as bad as he thought. He thought that Sirzechs had died and Kurenai told him that wasn't so. I'm pretty sure that the children know that they are within the barrier and that Azazel was killed fighting Trihexa. Again what secret is there? Basically everyone knows that all of the major gods and leaders are in the barrier with Trihexa. Grayfia saw Sirzechs and his peerage go into the barrier. Vali commented that they would be able to see Azazel again, although it would be thousands of years. Although Rias didn't see her brother go in there, she was told. What reason do they have to keep it from her. Or does she think that all of them died fighting Trihexa already? Does she think they're just sitting there having a tea party? Or that they died sealing Trihexa.

And plus Sirzechs, Serafall, and Falbium not being Maou in the future could be for any reason such as them retiring and giving way to the new generation. Azazel just assumed the worst.