Sakura and Shirou
As they stepped out of the registration centre, having assisted Nanako in registering herself as a citizen of the Nexus, Shirou heard the patter of feet heading in their direction. Realising that the person was about to collide with them, Shirou attempted to move out of the way, but he was too late, and he felt a sudden impact. Looking around, he saw a young boy, around 13 or 14, now sitting on the floor, rubbing his head. However, he quickly got to his feet and ran past them, demanding that they get out of the way.
Shirou and Sakura looked on with confusion, only to hear a shout from a nearby alleyway, demanding that they stop the boy, followed by two men rushing out, obviously chasing after him. They weren't sure what, exactly, the boy had done but, in a place like this, two bulky men chasing down a child were unlikely to have particularly good intentions. Even if the boy had genuinely committed some crime, they weren't willing to simply allow the men to get hold of him and enact their vengeance.
"Sakura, stop them!" Shirou said, quietly. "I'll go after the boy."
With that, Shirou set off down the road, using reinforcement and his generally higher speed to catch up with him quickly. Sakura, meanwhile, waited for the men to pass nearby, and reached out with her shadow tendrils, wrapping them around the waists of both men.
"Why should we stop him?" Sakura asked. "What has he done?"
Shirou, meanwhile, had caught up with the kid.
"Hey, stop!" he said, grabbing him by the arm. "What's going on?"