User blog comment:B214/High School DxD EX/@comment-79.50.160.94-20160130003159/@comment-3965848-20160130004602

Kiyome Abe might be one, plus there's also Bennia, Mira, Tsubasa Yura, Tiamat and maybe Ophis, although I'm just through every possibility I can think of and some of those might still be unlikely.

We could find out once the series ends though.