Rarity and Applejack stood before the Castle of the Two Sisters. Rarity had remembered there being a sparkly diamond inside the castle. But the last time they were there, they had seen a shadowy figure sneaking around, which they suspected was the real Pony of Shadows. So they had never entered again, besides, Twilight got her own castle not long after.

Applejack had been inside the room with the diamond in it more than any other pony, so Rarity asked her to come with her and show her to the room. They were wearing skintight black outfits similar to Celestia's from the previous chapter. They wanted to find the diamond without being seen by the Pony of Shadows.

They walked into the castle, and Applejack led the way. As Rarity followed, she realized she had not gone to the bathroom before she left, for she needed to pee.

Applejack led Rarity through a hall. "Shouldn't be much farther," she said, turning around to look at Rarity. She couldn't help but notice how edgy Rarity was.

Rarity wished they hadn't chosen to enter the castle after dark. This seemed the most likely time the Pony of Shadows would appear. She was very nervous about running into the Pony of Shadows. This wasn't helping her predicament. She didn't realize how badly she needed to go.

Applejack noticed the extreme discomfort in her face and said "If yah gotta go to the bathroom, there's one over there." She nudged her head toward a nearby door.

Rarity started to walk toward the bathroom, but stopped. "What if the Pony of Shadows catches me in there? I'm not taking any chances!"

"If she doesn't catch yeh now for how loud yeh're talkin'," said Applejack. "Well, have it yer way. But if you wet yerself here, ah won't mind." She blushed, hoping that didn't sound insensitive.

"Applejack have you lost your mind?" said Rarity. "I would never do anything so unladylike." She blushed, remembering her accident at the beach, but brushed it off and climbed onto Applejack's back so she was riding her. "Now you can run as fast as you can, and if I wet myself now, let's see if you don't mind it then."

Applejack said nothing, for the truth was, she wouldn't actually mind Rarity peeing on her. No pony had ever done that before. But she didn't want Rarity to wet herself if she didn't want to, so she ran toward the diamond room as fast as she could.

There was no sign of the Pony of Shadows when they reached the room. Rarity found the diamond in the middle of the room. She quickly dismounted Applejack, grabbed the diamond, and hopped back on her back. "Now let's get back to Ponyville, fast!"

Applejack ran as fast as she could through the castle. Any second now Rarity was sure the Pony of Shadows would come out, but there was no sign of her. It only took minutes for Applejack to reach the castle entrance, but to Rarity it took hours.

As Applejack ran out of the castle and crossed the bridge, Rarity really needed to go. She positioned herself so she was sitting sideways on Applejack's back and crossed her legs, grabbing Applejack's mane with one hoof and her tail with the other to keep from falling off, and setting the diamond in her mane.

As Applejack was running through the forest, Rarity said "Faster, Applejack!"

"This is as fast as ah can go while carryin' a pony," said Applejack. This was the honest truth.

"But if you keep running at this pace, I don't think I'll make it," said Rarity.

"Then just let it all out," said Applejack. "Ah don't mind."

Oh, you don't, do you? thought Rarity. Have you forgotten I'm riding on your back? She could hardly believe what she was about to do, but she knew she wasn't going to make it at this point, and Applejack asked for it! Rarity positioned herself so Applejack's back was between her back legs again, and let it all out in her skintight outfit. Rarity felt exceptionally foolish knowing she was wetting herself, and blushed beet red, but after the first ten seconds, she let out a sigh of relief. The release did feel wonderful after holding it in for what felt like forever.

As soon as Applejack felt her back grow wet, she stopped in her tracks, her heart racing. Rarity was peeing on her. No pony had ever done this before, and although she felt bad for Rarity, she couldn't deny to herself that she loved it. When Rarity sighed in relief, Applejack began to relax - Rarity was enjoying this, although she knew she'd refuse to admit it.

When Rarity finished peeing, the crotch, rump, and back legs of her outfit were soaked in urine, as was most of Applejack's outfit. "My apologies Applejack," said Rarity. "I didn't mean to... I couldn't hold it." She blushed, as she knew she could have held it at least a little longer.

"That's all right, sugarcube," said Applejack. "Ah'll get yah to Carousel Boutique and we'll get yah changed."

It was night, so they made it to Carousel Boutique unseen. As Rarity was taking off her outfit, she said "You know, I don't think there really was a Pony of Shadows. It was probably Pinkie Pie again."

"Or maybe that's where Tirek was hidin' out," said Applejack. "And at least yah got the diamond."

Rarity took the diamond out of her mane and set it on a table. "It is simply divine." She still felt a bit of shame, but looking at her prize made her feel better. "Now I need to take a long bubble bath. And let us never speak of this again."

Author's Notes:

I did this by request, and tried to add a little more detail than the previous chapters, particularly to the events leading up to the wetting. But I won't write any more unless I get a request for another specific scenario that's within my power.