Luna and Celestia have agreed that Luna needs to be more vocal in her feelings towards her sister. Well, by agreed this means Celestia pretty much ordered luna to write a ltter to her every month. Which of course, leads to Luna's current predicament and realization of what she wanted to say to her for all these years. Which comes from the help of an unlikely source.
One shot, not much of a premise for it. I just had this crazy thought of a dream and chose to write it up as best as I could before I forgot it.