User blog comment:Piyush Banerjee/Shin DxD 2 discussion/@comment-38501836-20190212124916/@comment-38501836-20190213120451

I've just been knocking the ideas around because among Issei's brides that aren't devils there are:

Kunou

Yasaka

Elmenhilde

Roygun

Le Fay

We know that Kunou and Yasaka won't join, Roygun is al;ready a king and if Le Fay joined (which she won't), she would be prime Bishop material

So that just left Elmenhilde, a knight or rook would work with her

Other than these women, all that''s left is to introduce new characters or less likely for trades to take place,

who knows maybe someone from Riser/Sona will decide to join Issei. although I seriously doubt it