User blog comment:FairyRaven/Fairy Tail Chapter 371: Tartarus Arc, Part 2: Song Of The Heavenly Dragon, Review and Commentary/@comment-24467372-20140214095355/@comment-4829046-20140214101825

Technically though it would work like some sort of magical operation where their bodies are altered to be able to use Demonic abilities so if Minerva can be called a Demon, then so can Mira.