Kiritsugu wasn't expecting that, but his expression doesn't reveal his surprise. He glances down at his hands. He was never able to make anything (excepting his daughter); his abilities had allowed him only to kill. When he returns his gaze to Archer, his expression is curious, maybe even faintly hopeful.

"Is that what you do, Archer?" There are still things he doesn't know about the man Shirou became. He does want to know more about him. This is still his son, after all.