User blog comment:B214/Volume 22 spoilers/@comment-14.201.211.143-20160910010909/@comment-124.149.182.246-20161001103621

Elmenhilde to me was unexpected, but ultimately good. I think her attraction to Issei is the result of being impressed with him from the events of Volumes 12 - 14 and the aura of the dragon that attracts females of other races.

Now given that Gasper (half vampire) took a bishop piece, or the equivalent of 3 pawns, and given that both of Issei's bishops are already taken, then she will be made a knight, also worth 3 pawn pieces. Traditionally, vampires are very strong (at least as strong as 10 men), very fast (seen as a blur to humans), very resilient with enormous stamina, regeneration, hightened senses, sight (particularly at night, maybe infrared) sound and smell, knife like finger nails (retractable presumably), turn into/control bats and mist and for some at least able to use magic. Hopefully, either through a mutation piece or artifical sacred gear, her weakness' of daylight, crossing moving water and needing to be invited into a building, can be overcome. Then add on a Knight pieces sheer speed and a devils demonic magic, then she becomes a very effective piece indeed.

Rossweisse becoming Issei's rook, this was also unexpected, but Rias has done a favor to Rose, in that she now has her permanent boyfriend/partner (and maybe latter, husband) in her new King, Issei.

Issei's peerage:

King - Issei

Queen - open

Rook - Rossweisse

Rook - open

Bishop - Asia

Bishop - Ravel

Knight - Xenovia

Knight - open (hopefully Elmenhilde)

Pawns - open (hopefully Kiryuu and the girls of the kendo club)