FimFiction Link - Short ID: 922/common-sky
Published: Sep '11
One of the oldest Tunafics on the site. It is a mostly nice read, and more, it is impressive how many core tropes it got right for its time. Once they're put together, Twilight and Luna stargaze, sleep together (don't worry about this one), have an omelette breakfast, bond over Luna's princess troubles in court, and Twilight gets to learn a spell from Luna. There are a lot of really cute sapphic scenes. Also, they sleep together (you can worry about this one a bit).
Unfortunately, the fic is severely held back by its age. Published not a month before Luna Eclipsed, such fics have to choose somewhere between the worst interpretation of her (no characterization whatsoever), or the best possible (an OC made entirely from whole cloth). Common sky splits the middle with a strictly canon Luna: the anti-Nightmare, Blue Fluttershy. Blue Fluttershy is timid most of all, and her singular hobby is being crushed by loneliness. As such, Twilight is responsible for driving 95% of any plot or interactions.
The prose is mostly good, with good perspective switches and long, introspective sections featuring your favorite purple pony. The most distracting mistakes are some lossily edited sentence fragments, and a propensity to use all caps where italics should be used. It also shows its age by including a comment from every M6 whenever it's possible to do so, although you can tell doing so goes against the author's natural sensibilities by how compressed they are. One thing that amused me was Twilight packing no food and correctly predicting that Pinkie would give her a pile of useless sweets for her cross-country trek, only for them to be promptly forgotten as Twilight then only eats reasonable food for the rest of the story.
Two more downsides to the fic are S1 Luna, and S1 Luna. Another piece of her old canon characterization is the childish idiocy inherited from NMM. Luna knows absolutely zilch about astronomy. This choice is in service to a common Tuna trope in which Twilight teaches Luna about herself, but it falls on its face. Definitely one thing that later Tunafics did better. And, of course, an on-the-moon headcanon providing for one line of cheap edge and nothing else.