User blog comment:B214/General Discussion/@comment-9595671-20160820093528/@comment-9595671-20160823042901

@B214: Depending on Bina, we might get those other mothers soon. So far I only see 14 girls who like Issei, and 2 of them (Kiyome and Tsubasa) may not make it.

Kiyome cause I think someone said Ishibumi lacks any plans for her, and Tsubasa... she's afraid of how the other girls may react if she did anything.

@Contributor: I think that's only the Devil's actually (correct me if I'm wrong), for Angels the problem is if they don't reproduce a certain way, they'll end up falling.

For the Fallen Angels? They don't have anything like the Evil Pieces or Brave Saints, so the only way for pure fallen angels to to increase in number is for or some angels to fall.