Hey, here to return a review for the holiday swap! :)
I'm really intrigued! This was a great way to start the story, and I feel like you balanced establishing the premise and leaving a lot of questions open really well, which can be hard to do. I'm still left wondering how exactly they lost their memories, how Ron and Hermione have gotten to the points in their lives they are right now, how Ginny and Harry's relationship has been going despite the tension from losing them... I could go on and on.
However, within that, you did give me enough information that I could fill in some of the blanks. Ginny and Harry are clearly having some issues with their relationship, probably in a large part because she's so preoccupied by something he sees as hopeless. Ron seems to be trying to just get on with it (as much as he can, anyway), where Hermione is clearly distracted and disconnected from her life.
Speaking of Hermione, I especially liked the way you depicted her relationship with her fiancé - there was just enough affection that the relationship felt genuine, but I also definitely didn't feel like her heart was completely in it. She's certainly not madly, wildly in love - which I guess is kind of the same problem Ron is having with Chelsea.
I do have a little crit, though - hopefully you don't mind and will not end up regretting swapping with me. :P
First: Your writing style is really crisp and readable, and you definitely pull the reader (or at least, this reader) into the story. However, I do feel like you sometimes go a bit overboard with the adverbs and adjectives when it's either unnecessary or there are better ways to get the sentiment across. For example, in the beginning of the chapter, I felt like you spent more time than you really needed to talking about the owl. A little more detail than "the owl flew to the window" can be a nice touch, but writing out every action can make it drag a little, and there are a few points in the chapter where that happens.
There are also a few points where I feel like you rush things, especially when Ron gets hit by the car. It was just all stated very plainly and without any real narration, and that was especially jarring because your narration in general was really solid. Off the top of my head (and I hope you'll forgive me for how awful this is - I'm a bit tired), something along the lines of, "Ron was so caught up in his thoughts that he didn't notice the gravel beneath his feet until it was too late. He heard the screech of the car's brakes and looked up just as it hit him, and everything went black." Does that make sense?
All in all, though, great start, and I really enjoyed reading it! :)