Luna motioned for her sister to lie on her bed, and when Celestia was comfortable the younger sister took out a set of four shackles, much to her sister’s surprise.
"Luna, W-What is this?" Celestia stammered.
"Just some precautions sister." Luna soothed, as she began to lock her sister’s hooves in them. "Nothing serious."
Soon, Luna had her older sister unable to escape the bed. The shackles and chains were magically enhanced, so the only way out was by key. Celestia decided not to fight it, in case her younger sister counteracted. Luna levitated over a large chocolate and strawberry frosted cake and offered it to her sister. The moment Celestia refused, she magically shoved a slice into her sister’s maw without a second thought. Celestia tried to fight back the helpings that followed, but each dessert or snack was shoved down her gullet and fell into her stomach. Cake, ice cream, cookies cupcakes, pies, candy, oat burgers hay fries, pizza, chocolates, donuts, carrot dogs, crackers, apple chips, apple fritters, apple dumplings, apple scones, applesauce, caramel apples, apple strudels, apple brioches, apple fries, apple turnovers, apple cobblers, there were too many things to keep track of as they were forced into her.
The more Celestia was fed, the more her body changed. Her belly ballooned out, to a slightly noticeable pudge, to a spherical swell that soon stood her up, and eventually ended as a ground hugging blob. Her face puffed up squishy cheeks that went from tennis ball stuffed to sagging and resting atop bulky shoulders, like medicine balls, and her chin gained two siblings which then merged with her chest and general neck fat which developed sloping folds that gave it an almost accordion look, then thickened so much that they covered her golden necklace. Her legs and thighs plumped up with drooping tissue that were like sleeves upon sleeves, up to the size of tree trunks. Her plot however was the one thing that her sister seemed to enjoy watching the most, as it bloated to rotund proportions, to jutting out like boulders heavy enough to crush the throne and ending up a few feet over her flabby back and covered in cellulite dimples.
After shoving one last cupcake down her sister’s gullet, Luna stepped back to take a look at her work while releasing the shackles and smiled in smug satisfaction. Her sister wasn’t an immobile blob, but a blob regardless. Her revenge on her “big” sister was complete. Now Celestia would probably know better than to prank the Princess of the Night.
"Wait until they see you now, sister." She thought to herself.