Rider instinctively tensed-up as Caster descended beside her, but she made no aggressive move. After all, he was Sakura's servant as well, and as long as he acted in Sakura's best interests there was no reason for them to fight.
She could tell from the way Caster and Sakura were acting that they were conversing mentally, but she had no idea what they were saying. She was rather shocked, therefore, when Sakura suddenly turned towards Caster and spoke out loud.
“Is there a problem with me contracting with Rider?” she said, clearly angry.
Rider knew, of course, that Sakura had intended for her to hear that. Otherwise, she would not have said it openly. But, she felt no need to intervene just yet. There was nothing she could add.
But, then, Faust materialised, before replying.
“Yes, there is a problem. You’ve just contracted with a servant that I just finished fighting. How do you know she’s not a threat. You say you know her, but does she have any proof that she’s the same Rider you know?”
Rider was livid at his response, and went to speak up. Before she could, though, Sakura got in first.
“How can you say that! She was trying to rescue me! Rider would never hurt me!” Sakura said, stomping angrily towards her other servant.
"Caster, you attacked me. I never made a single aggressive move towards you or Sakura, all I ever did was attempt to prevent you harming Sakura. I understand why you acted as you did, I would have done much the same if I were in your position, but you cannot blame me for a fight you started.
As for me being a 'threat', I have lived with and protected the Sakura in my world for over 30 years. This Sakura is not quite the same, but she is just as deserving of love and protection as the one I know. I accepted Sakura's offer of a contract because I know she wants and needs me to be here for her and because I care for her and wish to protect her in every way possible, nothing more. If you care for Sakura at all, you will respect her decision.
I will never harm Sakura. I would die before I allowed Sakura to come to any harm. I would do literally anything to prevent Sakura being harmed", she said, her anger at Caster's attempt to force Sakura to act according to his wishes and not her own clear.