User blog comment:B214/Volume 23 discussion blog/@comment-31764731-20170428154739/@comment-29963364-20170429014722

Since Tosca's Sacred Gear creates extremely effective barriers (no one could break it for all the years it was active), but also puts whatever's inside it into "stasis", Rias will likely make her into a Rook, or Bishop.

Just like how Rossweisse's defensive magic was made stronger by her Rook Piece, Tosca's SG barriers could be made stronger.

Or she could be a Bishop and use her barriers in a more "support-ish" fashion. Similar to how Sona's bishops placed a barrier around her to hide from Rias' peerage during their Rating Game.