Tied up is great! Tied up and balls separated even more fun.

I should also add a good ball buster can often inflict massive pain without much impact. I remember one session tied down on a bench, balls tied and separated and the Domme just kept hitting the same spot over and over. Not much impact but the same exact spot with a pretty fast frequency. One of the only times I actually cried in a session but I would say the injury risk was quite low but definitely maximum pain! Good times cool