Probably Shadowchild would respond to Kyubey the same way ze responds to gods in canon - which is to say, overwhelmed by the intensity of the light/shadow. What was the quote? Uh...
"The god there throws too much light. It makes the shadows sharp and dark, like holes in the air. I can't eat them all. If I went in there, it would be like trying to drink the ocean -- you drink and drink and you drown anyway, and the ocean isn't smaller afterwards."
I get the sense that Kyubey, as a being essentially on a whole other scale above humanity, would fit into a similar category.
Or maybe Kyubey's just the equivalent of a demon? They do seem to have similar disregard for the value of human life...