Alice has just met Bob, and although the two of them come from very different backgrounds, they have one very important character trait in common: Both of them have missing parents. It doesn't matter what the circumstances (although the circumstances might be very similar if only for plot convenience); one might have a Missing Mom and the other a Disappeared Dad, or maybe both of them have parents who were killed due to war violence, or maybe one or both of them never even knew their parents. Whatever the circumstances, this link between them is key to their relationship together.