User blog comment:B214/Volume 22 spoilers/@comment-30048084-20161031183100/@comment-87.8.65.94-20161112235854

We know what are the powers of vampires, and we know that the strongest vampire cannot be underestimated, maybe Elmenhilde has the talent to become one of the strongest pure-blood vampire and becoming a Devil (I guess she will become a Devil, obviously) would increase her powers. I think that Rook would be wasted for her current abilities, but a Pawn (no more than 2 pieces considering the actual level of Issei's power), would be good. Vampire have different kinds of powers and physical abilities so Promotion is the best ability for them.