On the night of the Canterlot Wedding everything was going right until two of the Bearers of the Elements of Harmony start dancing together. There's a bright flash of light and then two mares become one.
Turns out the Bearers of the Elements of Harmony can fuse together.
Turns out this isn't necessarily a good thing.
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This is a story taking the concept of fusion from Steven Universe, but not incorporating any of the characters. The current tags will possibly change depending on where I go with this. The Teen tag is for implied language, some sexual references (but no actual sex) and generally just to be on the safe side. This happens literally the night of the Canterlot Wedding so no Twilight Alicorn.
Edit: The sex tag is there because Rainbow Dash. Just Rainbow Dash... and her dancing.