Rainbow Dash isn't a pony who generally likes to sit around doing nothing, especially when there are big things going down. So of course it would be just her luck that she would end up watching the Map for ponies trying to change history, when Equestria is gearing up for first contact with an advanced alien race just outside. And it promises to be a monumentally monotonous task, as nopony has tried to change the past in over ten years.

Until now, that is.

As the last pony left aware of the changes, Rainbow needs to travel through time and use her own ingenuity combined with whatever she can scavenge from the various pasts to which she travels to defeat foes far more powerful than she could ever hope to be, all the while being careful to avoid altering history even further.
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This is a crossover with the first installment of the Journeyman Project trilogy of video games (and its two remakes, Journeyman Project: Turbo and Journeyman Project: Pegasus Prime. Come on, I couldn't resist that title.) It will loosely follow the plot of that game, so if you're familiar with it you'll probably have some idea where this is going.