User blog comment:Jopjopjop/Volume 18 Spoilers/@comment-24098614-20140716015517/@comment-73.178.133.185-20140716134038

@anon1

According to wikipedia, Gabriel is not called an 'archangel' in the Bible "but is so called in Intertestamental period sources like the Book of Enoch". From what I've seen, the term 'archangel' is a catchall used to refer to leading angels in the various levels of the angelic hierarchy (as well as the second lowest of them). Furthermore, it will be used by angels belonging to one of the groups such as the "Four Archangels" that serve as the basis for DxD's "Four Great Seraphs" or the "Seven Archangels" that are connected to the days of the week and the seven vitrues. The material surrounding the various angels and demons, etc. is quite convoluted, with them called one thing then another in the same source. (Also, the biblical Gabriel and angels in general don't have a gender, though it has been referred to as a man at least once).

Anyway, as B214 said, we're talking about the female Gabriel in DxD where there is only one archangel in existence, Michael, and who belongs to the "Four Great Seraphs" within the greater ten Seraphs that are the leading ultimate-class angels.