Vanilla Incest

“Now, Twilight, you may think you know a lot about this castle but I guarantee you I know more, now watch carefully, this may come in handy for you some day.” Cadance couldn’t resist the smugness in her voice over her little surprise.

Cadance reached a hoof under the center of the large nightstand next to the bed. With an audible ‘click’ the entire wall beside the bed rotated slowly around revealing a vast assortment of different types of panties. Many were thongs of various kinds but there were plenty of other styles as well, there were more regular cut panties, ones with no crotch, some made out of translucent plastic-like material and even some pairs that looked like they were made mostly out of precious gem stones.

This was all a bit much for Twilight coming now from Cadance, she would have once been a bit more confortable about this but Cadance was married to her brother now after all.

You, my favorite little filly, and I are going to have no end of fun tonight. “

“I’m really not sure...about...this” Twilight said hesitantly starting to loose her built up confidence.

“Twily...” continued Cadance in a gentler voice using Twilight’s older brother’s nickname for her.

“Help me choose and then I’ll explain a few things to you ok? Don’t worry everything I’ll tell you, you will be happy about.”

“Um, oh, ok...uh... Twilight said hesitantly looking over all the possible options.

“Well how about... oh goodness!” Upon further inspection there was a row of thongs on the far end of the wall from Twilight’s position that she now noticed had all of her friend’s cutie marks displayed prominently in the crotch. There was even a pair with her own cutie mark on them.

Cadance followed her gaze and laughed softly

“Ah yes thoes, has aunt Celly never shown you thoes before? Can you guess which one is her favorite?”

Cadance pulled the purple thong with Twilight’s own cutie mark down with her magic while watching Twilight the whole time.

“But it's a bit weird...” Let’s try something else...” Twilight suggested in a moment of confidence.

“No? Cadance said seemingly a bit disappointed, well maybe aunt Celly will get you to like them, maybe she’ll even make you wear them... Cadance remarked while watching Twilight out of the corner of her eye.

Twilight felt herself get even warmer with that suggestion.

“What are thoes, the small red ones? Asked Twilight.

“Oh these you mean?” Twilight responded with a nod.

“Well these are what’s called a two-way, it's a thong that's the same in the front as it is in the back. Quite enjoyable to wear, especially under one of thoes ridiculously fancy dresses I’m forced to wear at the stuffy formal dinners that the old unicorn aristocracy are so fond of. Really they do make the evenings more enjoyable. Especially as the longer you wear it the more it tends to work its way...up... into you.”

This revelation made some of Cadance’s facial expressions at thoes events considerably more understandable considered Twilight.

Over the next ten minutes or so they ran through a number of different options but eventually they settled down to two choices, a thong with a color scheme suspiciously similar to Rainbow Dashes’ mane and tail and a tight pair of panties made out of a very smooth and shiny light blue material that had three holes in it, one for the wearer’s tail and the other two presumably so that the panties would never have to be removed no matter what the pony wearing them might be doing.

“So which do you want me to have on during sex Twi?” asked Cadance holding up both choices in the air with her magic.

“I think, I think I’ll go with the blue panties.” Said Twilight

“I think they will be more convenient to use when we, um, when we...”

“Fuck? Twilight, yes we will do that, a lot!” Cadence grinned at Twilight with a look rather unbecoming a member of the royal family.