Sunset sprinted to the sirens' castle, ponied up, and blasted down the front door. To her dismay, ponying up did not dry clean her at all. She ran to the sirens' throne room as fast as she could.

All three sirens were inside waiting patiently for her.

"We hope you enjoyed the trip here," said Adagio.

"Of course, you'd probably say it stinks," said Aria.

Sonata laughed at this.

"Where's Princess Tiffany?" Sunset demanded.

"She's in the dungeon with many more of her most loyal subjects," said Adagio.

"Then all I have to do is defeat you and-"

All three sirens blasted Sunset to the ground immediately. Sunset's pony features disappeared. Aria and Sonata got Sunset into a chair and tied her hands to its arms. Then they tied her feet together.

"Surely you don't want me stinking up your throne room, do you?" said Sunset.

"We'll just leave you here till we have what we need," said Adagio.

"What are you after this time?"

"We found a source of magic that gave us power, which still didn't give us our old siren powers back. But I discovered there is an amulet that we can use to regain these powers. Once we have it, we'll turn everyone else in this world against each other and feed on their hate. Then it's back to your world, and then, finally, Equestria will be ours!"

Sunset struggled against her ropes. "I will stop you!"

"How?" said Adagio. "We sealed the way out. Your friends aren't going to help you. We want you to see us destroy it all before we finish you. Aria."

Aria held up two chunks of giant fruit that were each about the size of a regular fruit. One looked like a prune, and the other was a fruit Sunset wasn't familiar with. "Eat these," Aria said. "One of them will keep you full for a week. It's no good if you die before seeing our victory. If we don't find this amulet in a week, we'll be back." She held out the fruit chunks to Sunset, who ate them, and then Aria held out a glass of juice. Sunset looked at her suspiciously.

"It's not poison," said Adagio. "I told you we want you to see our victory first."

Sunset drank the juice. It tasted unfamiliar to her. "What is this?"

"It'll keep you hydrated for a week," said Aria.

"But it'll make you pee a lot," said Sonata. "And not diluted pee either like when you drink lots of water in one day."

"Have fun sitting like that until we get back," said Aria as she, Adagio, and Sonata flew out their window.

Sunset sat in her messy state, unable to move much, as the hours went by. Sonata wasn't kidding; that drink did make her pee a lot, even though she never got hungry or thirsty. Rather than give the sirens the satisfaction of letting her squirm again, Sunset decided there was no point in suffering, and peed as soon as she felt the urge grow strong. Between the state she was in and having already wet herself once on this adventure, there was really no point in trying to hold it. One couldn't even tell what color her shorts and tank top were.

That evening, she made a rather nasty mess in her already heavily soiled and smelly shorts. This had to have been why Aria gave her a prune. She had to sit in this state for the entire night, and for another whole day, peeing more times than she could count. But through it all she never lost her resolve to fight the sirens and save this world. As unpleasant as this was, she wasn't about to let it defeat her or break her will. She was tougher than that. Besides, she honestly found the Anon-A-Miss situation much worse.

On the third day, the sirens returned. Sonata giggled at the sight of the massive puddle under Sunset's chair. By now the pee smell was easier to notice amidst the other smells.

"That was faster than I expected," said Sunset, trying to sound unaffected by what they had done to her.

"We found it sooner than we expected," said Adagio. "And now, we shall use it to take control of the other two worlds!"

This was it. It was now or never. Sunset thought about her friends. About Princess Twilight. How she wanted their worlds to be free of evil like them. How she didn't want the sirens that had put her through all this to win. She could feel magic stirring within her, with a bit of a glow, but it wasn't enough to even pony up. She tried to channel the magic of the amulet with her mind, hoping she could get it to react to her instead of them.

Surprisingly, the amulet glowed and was pulled out of Adagio's hand over to Sunset, engulfing her in a bright light. Sunset's bonds were destroyed and she ponied up again.

"This cannot be!" said Adagio. "It reacts to you? How?"

"My determination must be stronger than yours," said Sunset, and she released a blast of magic, which hit the sirens and sent them flying out the window, disintegrating their wings.

They landed in a large, wet, stinky pile of horse manure. Aria stood up and tried to blast Sunset, but it wouldn't work. She tried to flap her wings, but they were gone. Sunset had taken away their power. Aria groaned and sat back down.

Author's Notes:

I know, the way she defeated them seemed a bit rushed and made less sense on her own, but I couldn't really think of how else it would work. We'll chalk it up to the amulet's power and her unbreakable determination to beat them, possibly even increased by what they did to her.