Sakura and Rider
Rider frowned on hearing Wynn's comment. She could see and hear Sakura's suffering, and she desperately wanted it to stop, but taking up the offer was risky. If she failed, then Sakura's current suffering would seem like nothing compared to what Wynn would inflict on her. Uncertain what to do, and sure that Wynn would force one of them to do it, she decided to allow Sakura to make the decision.
Sakura, meanwhile, continued to scream and moan, Wynn's tendrils continuing to torture and pleasure her. She saw the woman look over towards her, smirk and chuckle, saying something else she could not comprehend, although it seemed to be about her magic.
"Wynn would like to point out that if you were worth your salt as a shadow user, you would have retaliated by now", Emily translated. "She had such high hopes for you."
Sakura frowned, pain still etched into her face. She knew she could have retaliated, but against a being of this strength it would have been hopeless. She could never hope to win, and she had Rider there to fight on her behalf. She wanted to respond, but the pain was too much, even speaking was difficult. Before she could even attempt it, she heard a message from her servant.
Sakura, Wynn will accept my offer, but there's a risk. If I do not perform adequately, then she will torture you, as she is doing to me now, and force me to watch. I think I can succeed, but if you do not wish to take that risk then I will decline, Rider said, a sad tone to her voice.
Sakura pondered her words for a moment. Her pain-addled mind was screaming at her to do anything she could to stop this torture, but she also did not want to let this woman win and force her to betray Shirou. And, whilst her situation was decidedly unpleasant, she had suffered far worse in her time under Zouken's control. She could survive anything that Wynn might throw at her.
If you think you can succeed, Rider, then you have my blessing. And, if you do fail, do not feel too bad, I will survive anything she can throw at me, Sakura responded.
Her approval gained, Rider addressed Wynn, a pained tone to her voice.
"I accept your terms", she said.