The whole shebang
“Just what do you plan to do with me?” Celestia asked indignantly.
“Oh, not much dear sister. Just a little bit of payback, that’s all.” Luna smirked at her sister who lay on the floor, her hooves bound with magical tethers.
“Whatever it is that’s bothering you Luna, just let us help you. I can’t lose you to Nightmare Moon again!” pleaded the elder sister.
Luna's mouth fell open. “Nightmare Moon? Oh my goodness! No! No, not at all! I am not being controlled again, nor am I after your kingdom!”
“Our kingdom,” Celestia corrected.
Luna darted forward, her eyes watering. “Exactly! You and the citizens of Equestria have been so kind to me since my return, maybe a little too kind,” intoned Luna, hanging her head sadly.
“Then what do you want?”
Luna’s face broke out in a crimson blush, “Everypony has seen me make a foal of myself in public functions since my return from the moon. So, I thought a little public embarrassment for you might be appropriate as well.”
“Public embarrassment?”
“Yes! You just seem so perfect and calm about everything! Truly a paragon to our beloved subject... but I know just what your weakness is!” Luna proclaimed pulling out an ornately decorated book.
“My…. Diary?” Celestia asked, raising her eyebrows quizzically.
“Exactly! Being a princess, you are well versed in Equestrian traditions and customs, so there’s no way you’ll make a social blunder like me, but I know your secret weakness.” Luna flipped open the diary to a marked page.
“I never want to see a cake again in my life! Every city, every town, every dell, no matter where I go, ponies offer me cake and I just can’t seem to escape the accursed dessert! I just know this stuff is going to go to my flanks! I should order the soldiers to remove every last slice of cake when I make appearances.”
Luna snapped the book closed with a devious grin. “That’s right, dear sister, I know you despise cake! So…. I shall feed you cake! Lots of cake! Of course, this cake will not only taste horrible, but it’s sure to put quite a few pounds on your pristine flank.”
Celestia couldn’t believe her ears. She wasn't even sure of the words leaving Luna's mouth. Cake wasn't a new food item by far, but it had only been discovered by an ingenious earth pony after Luna's banishment. Surely she had been exposed to it since her return though... hadn't she? Maybe not...
“Cake? OH! I mean, oh no! Not cake! Anything but cake!”
“Mwhahahahaha!” Luna cackled maniacally, her laughter filling the spacious royal sleeping quarters. She reached down and touched Celestia’s nose playfully, “Don’t go anywhere.”
Celestia stared as Luna stepped out into the hallway. She didn’t like the idea of her flank losing its toned and firm appearance, but you know…. Cake. Suddenly the door swung open and Celestia’s eyes widened.
Luna walked through the door pushing an eight foot tall, five layer cake into the room. The bottom layer alone looked to be around four feet in circumference.
“Luna! I can’t eat all of that!” Celestia protested.
“Maybe not, but you are sure going to try!” The top layer of the cake engulfed in blue magic and started breaking apart.
“No! have you no heart, sister? Surely you aren’t this cruel!”
"Open wide, princess of the sun!” Luna used her magic to pry Celestia’s mouth open and pushed the cake forcefully down her throat. Celestia moaned in delight as the moist cake washed over her tongue.
“That’s right, dear sister! Writhe in agony! Strawberry! I remember reading how you thought it was the most devious and evil flavor of all! Also, I requested they make this cake with the highest fat content they could. It’s sure to add quite a few pounds when all is said and done.”
The cake flowed into her mouth like a river of delicious, fluffy goodness. She felt the pressure start building in her belly while Luna mercilessly continued her "torture". Before long the last bit of the top layer of the cake went down her mouth allowing Celestia a break. Luna walked over wearing a sly grin and poked her in the belly.
“I do believe you have let yourself go, sister. What do you think the press will say about this little bump here?”
“You monster! How could you do this to your poor sister!” The white alicorn shouted with a trembling lip.
Luna grabbed the next layer in her hoof and pulled off a slice. “I think I’ll take a more hoof on approach this time.”
Before Celestia could protest, Luna pushed a large slice in her mouth filling it with that sweet sugary flavor.
That’s right, eat it up! Eat up the vile cake!” Luna said, forcing slice after slice of the delicious dessert into her sister’s mouth. The white alicorn felt her belly bulge more and more with each bite, bloating her midsection outwards and tightening her taut belly even more. As Luna jammed the last slice into her mouth a look of satisfaction crossed her face.
“Well, dear sister, you look less like you’ve had too much cake, and more like you’re pretty far along with a foal or two. I can’t even imagine the headlines after this! I think you’ve learned your lesson,” Luna said, as she started pushing the cake out of the room.
Celestia began to panic, she knew she’d had too much cake already, but it was so good! In the end, gluttony won out over good judgement.
“Lost your nerve didn’t you little sis? I always knew you didn’t have what it takes when it comes to giving ponies their just desserts!” Celestia spat out.
Luna froze in her tracks. She turned and walked back over to Celestia. “How dare you! So you think I’m too soft do you? Well I’ll show you soft! Just wait until I get through with you!”
Using her magic, Luna lifted the rest of the cake from its stand and started breaking it up into little pieces like she had with the first layer. Celestia had no time to react as a steady stream of cake forced its way down her throat. She gulped repeatedly in an endless cycle as more and more cake forced its way into her. The magical tethers on her legs dissipated and she quickly discovered why. Her belly had grown to the point where her hooves could no longer reach around her massive gut. Still, Luna pumped more and more cake down her gullet swelling her belly larger and larger still.
"When I get through with you, you’ll be nothing but a cake filled balloon!” Luna shouted.
Celestia couldn’t even bother to care. She was in absolute heaven as bite after bite and pound after pound filled her already massive belly even further. Before long, the only thing she could do was rub her protruding gut, feeling it squish and give beneath her ministrations. Rising like a loaf of bread in the oven, Celestia's belly grew further and further out of control. She moaned in delight as she pawed at her swollen paunch, now reaching five feet in the air.
During her vicious feeding, Luna realized she had a bit of frosting on her hoof and curiously gave it a lick.
“This tastes… magnificent! Confusion crossed her face as she stared at the blimping form of her sister before she realized she could hear what could only be described as sensual moaning.
"Tis a quandary. Why would my sister hate such a delicious dessert, yet sound as if she were taking pleasure from it?” Luna stared as the last bit of cake pumped its way into her sister. Celestia’s belly quivered with as the flow stopped leaving the princess of the sun a seven foot spherical parody of her normally regal self. Luna pushed her hoof into the bloated alicorn's gut, feeling it squish and earning her a pleasured moan.
"You... don't actually dislike cake... do you?" Luna asked, narrowing her eyes in suspicion.
Celestia's cheeks bulged for a moment as a gassy burp escaped her lips. "It's totally the worst... you should... you should get some more. I've been really bad. This is probably the best way to punish me," Celestia moaned out as she rubbed her taut and expansive gut.
"Ugh! I can't believe this! I can't even get revenge on you correctly!" Luna said with a huff as she started for the door.
"No, wait. You should *buuurapt* get somepony to rub my belly. That'll teach me a lesson for sure," Celestia called out.
"Goodbye sister. I'll send somepony up later to roll you into the shower," Luna said, slamming the door behind her.
Aiming her horn at her bed, Celestia pulled down a pillow and the satin sheets off her bed. After tucking the pillow behind her bed, she draped the sheet over her swollen belly and sighed.
"This is one punishment I don't mind sleeping off."
Closing her eyes, Celestia lay her hooves upon her taut belly and sighed as she let sleep overcome her.