The white alicorn pressed on the front of her pullups. Her bladder kept getting fuller and fuller, and her sister didn't show any signs of being anywhere near done.

"W-will it be much longer?" She asked.

"Most certainly." The blue alicorn replied dryly, sitting on the pink potty, taking her sweet time.

Celestia began nervously pacing back and forth in the room. Her immense need to relieve herself made her unable to stay still.

"H-how about now?" She asked again, hardly letting any time pass at all. The amount of time that had passed wasn't enough to change Luna's response. It was however enough for Celestia's bladder to get noticeably fuller, overhydrated as she was. At that rate she wouldn't have much more time before being forced to use her pullups.

"The less thou ask, the sooner we'll be done." She replied solemnly, seemingly having no empathy for her very desperate sister.

"Can't you hurry up?" Celestia insisted in a hopeless attempt to get Luna off the potty before she had an accident. She crossed her legs and began bouncing in place, trying to keep herself from wetting her pullups.

"Thou art aware we don't like to rush our royal needs."

"B-but they released this new banana flavored soda and it's s-so delicious! I c-couldn't help but have a fifth can!" Celestia tried to get Luna to understand just how urgent her situation was. She pressed on the front of her pullups with both her front hooves and shifted her weight from one hoof to the other.

Luna, however, was unmoved by her explanation. "Well, thou art the big sister, so thou should be able to wait for thy turn to use the royal potty."

"L-Luna! I need to use the potty now or I'm going to have an accident!"

"Hold it like a big filly."

And just like that, Celestia was left to continue her potty dances. Soon enough, she'd be unable to hold it any longer and her accident would cause her to be put back in diapers, leaving little to show she was the big sister of the two.