User blog comment:FairyRaven/Fairy Tail Chapter 365: Fairy in the Jail!, Review and Commentary/@comment-24257713-20131229050248/@comment-1359322-20131229162344

@Raven, that's where you're wrong, Kyouka probably tested beforehand whether or not Erza and Mira is suitable to become Demon or not and probably planned on erasing their memories and make them subordinates under Tartaros. That's way better than wasting 2 valuable talent.