When Starlight Glimmer reads A Hearth's Warming Tail for herself the day after Hearth's Warming, she finds it to be a bit different then how she remembered. Specifically, what was Sunburst doing in the story?
Starlight Glimmer, after spending Hearth's Warming in Ponyville, goes to the Crystal Empire to spend the New Year with her old friend, Sunburst, for whom she has also secretly has feelings. Can she tell him how she feels?
It started when they were children, when every sorrow could be ease with a hug. Eventually it turned into blind supplication and a race against her very bones.
After the crystalling, the banquets, and the private after-party, Starlight gets her chance to be alone with Sunburst. They realize that they share two things in common: their friendship and different perspectives of the day he got his cutie mark.
(Sequel to "Starlight and Sunburst's Misadventures in Flurry Sitting". Takes place after "A Horse Shoe-In".) Trixie takes it upon herself to set up a date for Starlight and Sunburst, since the two haven't had one in a very long time.
Long ago, the stars disappeared. Then, somepony returned them. You won't find the tale in history classes or archives—only in the hearts of the mares who were there.
Starlight Glimmer and Sunburst are new parents. They are also immensely powerful unicorns with a penchant for going overboard. These things don't mix very well.