User blog comment:B214/Volume 22 spoilers/@comment-24583889-20160803184150/@comment-73.46.6.122-20160803195335

That actually a good question seeing how rare mutation pieces seem to be. Rias had 1(bishop), which became five(four pawns added) due to issei's evolution, sirzechs had one(rook), and sairaorg has one unused(pawn), while sona's has none, which begs the question on how rare they are and if issei has any and/or if traded any to rias when got asia, rossweisse, and xenovia?