Rias Gremory is a strong fighter and she can fly which is always useful in a fight. However, Bass can fly as well and he even has super speed to help give him even more of an edge. I can say with certainty that having a crazy amount of speed and power at your disposal is usually enough to claim victory. Rias won’t come any closer than the other opponents who have gone up against Bass, but at least she’ll try her best. Bass wins.