We have said it time and time again. Big tits are big targets. Iona Grace came into this knowing what to expect but it didn't make it hurt any less. Her breasts are getting tied off right away and it will be a long time before they are set free. Every second they spend in bondage makes them more perceptive to every sensation.
Iona openly admits that she is a dirty slut who loves to cum. As her body is wracked with orgasms the weights that PD has clamped to her chest begin to jiggle and swing. This is enough weight to make those orgasms a bitter sweet experience.
It is like that for her all day. PD has so many great ties in mind. Every one of them puts her into a different predicament where squirming and resisting provide their own forms of torment. And then the most intense vibrations of her life hit her clit and what is she supposed to do? She can't help but buck when she cums and the way that hurts her just makes it that much harder to stop.