This is a great concept. Luna's a very interesting character and this story delved deep into her personality and her desire for redemption. Having Celestia orchestrate the Elements of Harmony and Luna's return is a clever idea, as well.Your writing and wording is great, but a few things stick out. To start off, there's the letters that Celestia sends to her sister. They all end with the capitalized, center-age 'CELESTIA.' It just seems to look a little out of place.The letters and the notes Luna makes to herself could use some indication that they are different from each other, even if it's just something small. It would just make it easier to follow.The last bit of oddity is your day choice. By day 400 Celestia has taken on Twilight as a student. That makes Twilight roughly 999 years old by the time of the first episode. Also, all of the other mane six seem to be around at day 800. They should probably only start showing up much later, ten to twenty years before Luna's return, depending on how old you think each of the mane six is.But, yeah, that's my two bits. You can take it or leave it as it's your story, a good one at that. It's a great idea for some Luna character reflection, I just think it could use some polishing.I hope I don't sound too pushy or arrogant. I'm really not trying to be, I swear. I, myself, am pretty new to fanfiction, so take what I've said at face value. I hope it helps.
No that's fine. Thanks for your input. When you come to think of it though, a lot of the ponies must be older than they seem, like Pinkie Pie. She's been around since G1.But I'll try to make it better.