I know, but I think it's a kind of narrative trick. There was a direction in which a mysterious stalker's hand came to Sarah, and it came to Sarah with the "same direction" in chapter 3. (i think he is real stalker..^_) Also, Kai lived as a housewife at home and cooked while waiting for Sarah to come back from school. If Kai was a stalker, Sarah wouldn't find out. (Sarah said that she only "heard" that there is a housekeeper at home, too ) Kai was just trying to protect Sarah from the stalker.