Rider
Rider smiled as she followed Sakura and Shirou down the stairs, glad to see her so happy and excited for the trip. However, as they reached the bottom of the stairs, they met Rin and Archer waiting for them. Rider could tell that Shirou was wary of the other servant, attempting an awkward bow as he greeted him politely, and Sakura evidentially also noticed it.
As Shirou addressed Archer, Rider noticed a momentary flash of anger over Archer's face, causing her to tense up in case she was forced to defend her master's beloved. Her discomfort increased as she noticed Sakura pull her lover behind her reflexively and she stepped forward protectively, taking a place next to and slightly in front of her master, ready to attack if ordered or if Archer made any sudden moves. Fortunately, though, the other servant's anger quickly disipated and, instead of attacking, he bowed and responded to the greeting in kind, his expression unreadable. Letting out a sigh of relief, Rider relaxed a little, however, she could tell that her master was still rather on-edge.
Sakura, clearly uncomfortable with Archer, instead addressed her sister, informing her that they were going out and why. Meanwhile, Rider had a thought.
Wait, I need a phone that works here, so I can contact my former master and make sure she is OK, she thought.
Seeing no need to add anything to Sakura and Rin's discussion, and not wanting to address Archer in front of Sakura, she instead turned to her master.
"Sakura, when we are out, I need to find a new phone, or a SIM card for my current phone", she said, taking the futuristic smartphone out of her pocket. "My current phone doesn't work here...."