User blog comment:B214/Shin DxD 1 discussion/@comment-73.49.228.11-20180805181343/@comment-34061653-20180805182757

Rias made it clear in volume 23 that she will not use that sword. Furthermore, Rias is not a swordsman nor has she ever used one as it is not her fighting style. Rias is a wizard-type and a long range fighter.