What if ponies did poop rainbows? What would happen? What if only one pony pooped rainbows? What if that rainbow poop proved to be an incredible source of near limitless energy?

One day, Rainbow Dash looked down after recently using the restroom. To her surprise, her feces was multicolored. Twilight begins to experiment with the promising substance, only to discover a way to use it as an incredibly powerful energy source.

Rating Teen and Sex just to be safe. It talks about it (in a very scientific sense) but does not show it.