While adjusting to being a human for her first time in the Equestria Girls world, Twilight Sparkle also has to figure out how to use the bathroom correctly. Given that Equestria also has toilets, this wouldn't be much trouble - except for an unfamiliar piece of clothing she is wearing under her skirt.
Contains: Wetting and underwear. Might actually be tame enough for a T rating but I'm playing it safe, and while primarily written for fetish purposes, could be seen as bathroom humor as well.
I thought this would be an interesting story to write because we could actually see this happening behind the scenes. Quality might still be lower, though, and again, don't take too seriously.