"Caaaakeeeee..." Celestia moaned. She knew it was bad for her but she just couldn't resist. "At least I'm an Alicorn! We don't get fat." She then continued to scarf down cake after cake after cake.
Pausing for a moment, she looked at herself in the mirror. Sleek and slim, the image of perfection. The only sign of her cake habit was some frosting on her lips. "Yep, skinny. Now back to the cake!"
~Discord~
Discord, Lord of Chaos, was flying around thinking of pranks he could play on Celestia. "Let's see. She is addicted to cake, but can't get fat, being an Alicorn. Hmm.... I think I should change that...."
He chuckled evily, smirking. "I think she deserves some 'special' cake. Courtesy of me...!"
~Celestia~
Celestia was just finishing her last slice of cake when someone knocked from outside. Quickly wiping her face, she called out. "Who goes there?"
In response, her cake delivery pony called back. "It is me, Princess! Have a few more cakes for you, special delivery!"
Celestia opened the doors with her magic, thanking the delivery pony and taking the cake. Returning back to her bed, she looked over the package of cakes.
A tag on the box said. "Hey Cely! Heard you like cake, so decided that as your (late) birthday gift I'd give you some of my special cakes! The flavor is unmatched by any other!"
"I don't particularly trust Discord, but... it is just cake. What could go wrong?" Celestia mused. Famous last words.
Opening the package, Celestia's eyes were treated to several massive cakes, delicately decorated and no doubt amazingly flavored. Mouth watering in anticipation, she levitated one of the cakes out, placing it in front of her.
Quickly cutting a slice, she brought the cake up to her mouth and closed her eyes. "This better be good!" Celestia said, taking a bite.
Her eyes flew open instantly. The flavor was amazing! Sweet and rich, light and fluffy, too amazing for words! A tingling heat ran from her stomach to the rest of her body. Moaning in ectasy, she took another bite, and another. Soon, the slice was gone, and she was on her second.
Without pause, she dug into the entire rest of the cake, savoring the flavor. A burning heat was rushing through her body, making her moan and groan in pleasure. Her only thoughts were of the delicacy before her, and she was safe in the knowledge that Alicorns couldn't get fat.
All too soon, the first cake was gone. A burning, tingling heat covered her entire body in a blazing inferno. Celestia paid no mind to this, only thinking of eating more of the indescribable deliciousness. Never stopping, she flung herself into her second cake, feeding the erupting heat that was liquid fire through her body.
In no time at all, all four cakes were gone, fallen prey to the inferno in her belly. Laying back, panting, Celestia relaxed, only then noticing the fire inside her.
The inferno erupted, searing every part of her with the heat of the sun. Screaming a final time in ectasy, Celestia blacked out.
~Discord~
The Chaos Lord doubled over laughing. "I knew she liked cake, but not THAT much! Once the spells kick in, she'll be as big as a blimp! No more 'Sleek and skinny Cely', they'll be calling her Fatlestia or something!"
Snapping his fingers, he woke Celestia up and set his spells in effect.
~Celestia~
"Oof..." Celestia groaned, rubbing her head with a hoof. "That's a first for me, eating so much cake I black out!"
Noticing again the raging inferno inside her, she paused. "What's happening to me?!" She exclaimed. Lurching up, she stumbled to the mirror. Reaching it, she stopped and stared at her reflection.
She was glowing, and not just that, but growing. Almost indiscernibly, her body was swelling. With each heave of her chest, her belly rose out a tiny bit more. Her head was already resting on a double chin, with a third and fourth chin already forming. Her legs were being swallowed up by the expanding fat of her belly, the legs themselves thickening to tree trunks. Her wings were also sucked into her flabby skin, just the tips sticking out. Her cheeks were puffed like bowling balls, and all over she was expanding even more!
A minute later, she was the size of her bed. A few minutes more, she outgrew the mirror. Trying to turn her head to look back at herself, she found she couldn't. Her head, wings, and legs had all been completely swallowed up by the massive blob of fat that was her body. Gasping for air, she managed to yell one last word before she was completely turned into a massive ball of living lard.
"DISCORD!!!!!"