The Agony of Choice
In this scenario of your story, the protagonist is forced into a mechanical and psychological dilemma.
Her feet are slightly elevated, and her nipples are attached to her big toes with taut ropes. Any slight downward movement of her feet results in extreme pulling and painful stretching of her nipples. This forces her to keep her feet tense in the elevated position.
Vibrators are attached to her breasts, vagina, and anus, which can only be activated by placing her feet completely on a copper plate lying on the floor. However, this action has a painful consequence: When she places her feet on the plate, the ropes on her toes become extremely taut. This pulls her nipples so hard that it causes excruciating pain.
A button on the copper plate must be pressed to activate the vibrators. At this moment, the game becomes a true "agony of choice." She must decide between two extremes: the painful sensation of orgasm or the painful sensation of stretching.
Additionally, copper wires are attached all over her body. When her feet are on the copper plate, these wires deliver electric shocks that, at the moments when the vibrators are at their most intense, prevent orgasm and heighten the tension. The electric shocks serve as a further punishment, forcing her to question whether the pain of not reaching orgasm is worse than the physical pain associated with it.
This method combines pain and pleasure in an unprecedented way. There is no escape. She must either submit to the extreme pain of her nipples or the extreme pain of the electric shocks. It is an unstoppable cycle that can only be broken by submitting to her partner.