From the Animeraider:

Going back to when she was an infant, whenever Miori had something bad happen to her or something go wrong, a boy a few years older would suddenly appear and save her. She doesn’t even know who he is, and yet he somehow always appears. And then one day the two of them are thrown together at school and she discovers that his name is Haruka, and he has shadows all over his past but he knows that he’s supposed to protect Miori…