Another thing I mentioned, which could be me hearing things: When I watched some friends play through the intro the other day, I thought heard the main character say the word "ico" (if pronouncing it EE-ko) when he said "She was sacrificed because she had a cursed fate." I immediately thought: She was sacrificed because she was ico.

That'd be pretty cool if true, explaining the title of the first game (ico is not the boy's name, but the name of his condition) and giving weight to this idea of an implied shared background.