The strange girl turns out to be Mei, Naru's little stepsister.  All of her plans are about getting Naru back home so that she can go as an exchange student to Canada.  That is why she wants to get Keitaro and Mutusmi together, so that Naru will have no reasoni to stay.  Naru soon discovers a scrapbook left for her by her sister and finds a picture of herself in front of the Hinata Inn as a child.  What's more, there are two other children in the background that look awfully familier.