"Luna, please don't do this to me."

"I'm dreadfully sorry dear sister, but you've left me with no other option."

"P-Please I beg of you. I'll do anything: help wash more of the dishes, do your laundry, even repaint the throne room."

"I am sorry, but my mind is set."

"I-I beg of you. Don't put me on a-a.....(gulp) I can't even say it."

"A diet."

"Oh myself."

Celestia fainted backwards and landed on her soft yet firm queen sized bed.

"Stop being so......how do they say it? Dramatic. Tia, we have been participating in the exercise program for quite some time now thought you have yet to lose a single pound or an inch off your waist."

"What can I say? My body is just to perfect to be changed, the universe just loves every inch of me." Celestia said as she stuck her tongue out to tease her sister.

"Oh? Does the universe love this mountain of a ass you've acquired over the years?" Luna said pointing at Celestia's most treasured asset.

"It must, and it took a long time to get it like this."

Celestia grabbed her giant ass in both hands and moaned as she felt her own unique softness.

"Sister be serious!" Luna said swatting away at Celestia's hands.

"I am. The program just isn't working I'm afraid."

"It does for me."

Luna pulled up her dark blue dress to show her older sister her smooth, well toned thighs. They were well shaped but still retained the fat to give them a fuller look. She continued to pull the dress over her head and dropped it on the ground leaving very little covered, after a single month of exercising she grew from a skinny mare to practically a supermodel status. Her plump yet muscular thighs tends to attract some onlookers on a daily basis, her flat stomach that known to glisten with sweat during her jogging routine, and her humble double DD sized bust completed the look.

"I-I stand corrected." Celestia said blinking twice. "It won't work for me I'm afraid. We just have to accept it."

"Hmm. Maybe not."

"Huh?"

"Perhaps along with your dieting I can find a spell to increase fat burning."

"I suppose there's a spell book in the Canterlot archives."

"Perfect, I shall return with the spell."

After slipping back on her dress Luna left the bedroom leaving Celestia by herself, she turned to face a nearby mirror. Luna has complained numerous times about how big her ass has gotten over the years, so big that it started to bump and knock over everything as she walked the hallways. Vases, tables, picture frames, even prince Blueblood once. She even had to order a bigger throne to accommodate her. Celestia prodded her right cheek with a finger causing it to wobble, she gave it a soft smack and it jiggled wildly like. She blushed madly at how sensitive her skin has gotten.

"I suppose Luna is right, this has gotten out of hand. It's time for me to.......(gulp) diet."

She immediately vomited in the nearest waste basket, outside her room door however was the god of chaos himself.

"Hmm? Celestia? Dieting!?!? Oh no no. This simply won't do. That blessed ass is an Equestrian treasure and is a reformed spirit of chaos it's my civic duty to protect it at all costs. Now, what to do?"

Suddenly a cartoonish light bulb appeared above his head.

"Goody, a snack." Discord said taking the light bulb and eating it in one bite. "Wait a minute. I have an idea!"

A candle appeared on top of his head this time, his licked his bear paw and doused the candle.

Discord reappeared in the Canterlot archives a few minutes before Luna could get there, he scanned through the book selection.

"Now where is it........aha!" He said pulling out the spell book and blowing on the cover causing a large dust cloud.

He stepped out of the cloud through a door that cartoonishly appeared and began coughing.

"Blech. Why does this dimension's dust taste so terrible? Anyway let's take a look at this." He said as he began flipping through the pages. "Hmm. Fire breathing spell, wall climbing spell, ah here it is the weight loss spell."

With a snap of his, uh, "fingers" a feathered quill pen and a bottle of white-out appeared and floated next to him. He dipped his bear finger in the white-out and covered up the entire page. He tapped his chin with the pen deciding with words to put in replacement, he smiled as evilly as the Grinch when a few words came to mind.

"Annnnnnnnnnnnd that should do it. I've really outdone myself this time." He chuckled evilly to himself.

He set the book back where it was and disappeared in a flash, a few seconds later Luna entered and immediately found the book. Not taking a moment to read it herself she ran out the Canterlot archives with it in hand. The moon princess wasn't entirely surprised to see her sister raiding the kitchen fridge again for the third time this week.

"Ahem."

Celestia bumped her head against the top of the fridge not knowing of Luna's presence, she smiled sweetly at her sister.

"Oh don't mind me just grabbing a snack is all."

"Cake? For a snack?"

The sun princess smiled sheepishly.

"Fear not sister for I have the spell."

"That exists? I mean uh joyous news."

"Let us begin."

Luna opened the book to the page and quickly it read over.

"Huh? Well this can't be right."

"What is it?"

"This spell....is of a language I am not familiar with."

"It's an old book Luna, a lot of them are in different languages throughout Equestria. Doesn't mean the spell won't work, correct?"

"But I can't understand it."

"Try your best, if anything goes wrong we can summon Twilight and her friends like always."

"I suppose. Alright then, here goes."

Luna's horn glowed bright and she aimed it at her dear sister, Celestia silently gulped but made sure she didn't look afraid. Luna fired the beam, as soon as it hit Celestia the room was bathed in a bright flash. When Luna opened her eyes she found her sister lying on the floor unconscious.

"Sister! Sister speak to me!"

"L-Luna?"

"Yes, I'm here. I'm so sorry."

"No need."

"Huh? You're okay?"

"Okay? I feel.....great! I have so much energy right now! I-I want to go jogging! Luna are you going to join me?"

"Of-Of course! Let's go right now!"

"Great! Race ya!"

The sun princess dashed out the kitchen leaving Luna somewhat surprised yet really happy.

"Wait for me!"

By the time the two came back it was nightfall, both were practically sweating a river soaking their jogging outfits.

"That was a great afternoon of jogging sister, we simply must do that again someday."

"Absolutely I-(yawn)."

"Sister?"

Luna turned around to see her older sister had fallen asleep on the hallway floor with a little bit of drool coming out of her mouth, she laughed to herself and used her magic to levitate her sister to carry her to her room. Luna tucked her sister in for the night and decided to turn in early herself, she had to be on dream patrol the moment nightfall comes. Hour later Celestia woke up to a growling stomach.

"Oh dear, I didn't eat anything at all the whole time I was with Luna. I suppose no pony would mind if I had a quick midnight snack."

She sneaked out of her bedroom and headed straight for the kitchen, she was surprised to see one of the lights were already on. Underneath it was a plate of vanilla strawberry frosted cake sitting on a wooden stool in the middle of the kitchen, Celestia's absolute favorite dessert.

"I wonder who left this here? Hmph. Probably Luna trying to test me again. Well I know that I'm on a diet now and I plan to stick to it."

She instead went for the fridge picking out some fresh apples and water. She set the apples on the counter and facing the opposite direction of the cake and it's temptations. She quickly ate the apples but her stomach rumbled again, louder even. She turned to face the cake, and quickly turned away just as fast. She began guzzling down her water hoping that should fill her instead with no luck, her belly still hungered for more. Her eyes grew wide as she heard laughter coming from behind her, she turned around but saw no pony else. It was just the cake.....sitting there.......with all it's frosting.....and strawberries.

"Oh, I can't resist."

She got up, walked up to the cake, and decided to cut a piece. She stuck the piece in her mouth and moaned at the sweet heavenly taste, it was unlike any other cake she had ever tasted. She ate enough piece and another to the point where she was plainly devouring it. She was so lost in it's pure goodness she didn't notice that her ass was jiggling on its own as if happy to see it's owner enjoying herself one last time.

"So good!" She moaned between bites.

A good few minutes passed by and the cake was entirely gone, Celestia sighed happily. Now with a full belly she decided to go back to bed, once she returned to her bed chambers and walked past her mirror....she froze in place. Her jogging pants had tears in it meaning her ass has earned some inches and now stood a solid foot from the rest of her body. And that's not all her natural motherly thighs had some fat added to them as well and her already impressive F-cup jugs had grown to an unbelievable H-cup stretching her T-shirt to its limits.

"That cake did more damage than I thought, I can't let any pony see me like this I-(yawns) I suppose I could sleep on this for now and try to find a solution in the morning."

"Tia! Are you ready for another day of-"

Celestia woke up to see a frozen Luna standing in her bedroom doorway.

"L-Luna! What are you doing up so early?"

"Tia, what.......happened to you?"

"I don't know, I....woke up like this?"

"You do know what this means correct?"

"No, what?"

"This.....means.....war. From now on I shall be your fitness instructor and we will do things my way."

"Oh dear."

For the whole day Luna made Celestia run on a treadmill nonstop and had her eat nothing but carrots and celery sticks. Despite having this inflated ass her energy levels were still sky high and not to mention her sex drive has also increased greatly. The guards could barely keep their eyes off that jiggling monster watching it nosily slosh side to side and to see it glistening in sweat caused several guards to pass out from loss of blood flowing to their heads (the 2nd kind). Even Luna herself couldn't help but look at the mesmerizing cheeks as they did their dance. She snapped out of it when she though she saw her sister whispering to it as she massaged it. Daylight fell and the castle was asleep, Tia slept in her bed when she was awaken by the sound of her stomach growling again. She looked down at her still jiggling ass and smiled.

"It's time for another feeding my beloved pet." She whispered as she gave it a nice rock hard slap, it bounced and sloshed with joy.

She slipped out of her room wearing nothing but her bra and panties. Repeating last night's actions she sneaked into the kitchen with ease and noticed the light was on again, she looked inside and gasped to see two smaller cakes side by side sitting a wooden stool instead of one. She licked her lips as she picked up one cake and ate it in one huge gulp, her belly gurgled happily satisfied once again. She then looked at the second cake that looked liked it had slightly more frosting than the first, she licked her lips again.

"No, that's enough for tonight." Tia said placing the cake in the fridge as her belly and ass protested with sad gurgles.

Their cries grew louder as she stepped away from the fridge, she even thought the cake itself was feeling left out.

"On second thought, I suppose you did earn a little bit more Tia." she said with an evil smile.

On that note she devoured the second cake, her belly and ass jiggled happily.

"Yes, yes. Mama loves you too." Tia cooed as she massaged her fat ass.

The next morning Luna stared in disbelief to see her sister laying on the kitchen floor wearing nothing but her underwear.

"T-Tia! How could you!?! And after all we did yesterday!"

Before Tia could say a word Luna stormed out of the room, she looked down knowing she let her sister down. Her ass jiggled in response, she turned around and was stunned by what happened next. Her ass exploded from her panties as her goddess like thighs rubbed against each other and her bust size erupted from H-cup to a killer K-cup.

"N-No, this is too big. Far too much."

Her belly gurgled in response her bust shrunk back to a H-cup and ass deflated a bit allowing her to get up.

"That's more like it I suppose."

Now being able to move she ran after Luna, figuring she would most likely run to her room Tia decided to check there first.

"Luna? Are you in here?"

There was no answer. Suddenly the door closed itself shut and the room was bathed in an eerie green fog, stepping out of the fog was Discord himself.

"Discord?"

"Sorry, I ate a bean burrito earlier."

"That's disgusting."

"Don't worry I got it."

With a snap a large industrial fan appeared and rid the room of the fog.

"So Tia, how goes the dieting?"

"Not so well, I've upset Luna."

"Well that's to be expected."

"Yes I-wait, what do you mean?"

"Well........"

"Discord, what did you do?"

"I may have.....tweaked the spell she used on you a bit."

"You what. Why would you do that?"

"To protect the most glorious treasure in Equestria."

"Which would be?"

With a snap of his fingers Tia was spun around and was bent over her sister's bed presenting her plump ass to him.

"Dat ass."

"So this is your doing, color me shocked."

"In fair honesty you should've expected this, you know I'm the most dedicated ass man in the universe."

"Really? Tell me ass man: think you can handle all this?"

Clelestia smacked her right cheek creating a sea of ripples, all Discord could do was stare.

"You do know how to tease a man Tia."

"And I do it so well. Not to mention feeding this ass, mmmmm."

She gave the left cheek a smack, her ass jiggled and sloshed happily loving the attention it was getting.

"Yes, it must've took quite a bit of doing to fatten this ass up to this size. I should know."

"So it was you who made the cake also?"

"Surprised by my skill?"

"Mmmm. They were delicious." Tia said licking her lips.

Discord slapped her ass in response, another wave rippling through her sensitive skin.

"Oh my, take me Discord. Conquer my fat ass!"

"I plan to do so my dear. But not in this form."

"Huh?"

With a snap of his fingers his fingers he shape shifted into a new form, he was now a bronze skinned muscular sky scraper of a human man.

"Discord. Me likey."

With that said punctured his rock hard cock into her massive ass and began to slide in and out. The pace grew faster with every thrust, Celestia moaned in pure ecstasy as Discord enjoyed watching her fat ass cheeks slamming back into him. About a half our of endless rutting later he came inside causing her belly to expand outwards as it was filled with endless cum. Discord's new and improved body grew limp and he fell to the ground, Celestia giggled right before she sat her massive ass on his chest.

"I love your ass Tia." Discord sighed.

"It loves you too." Tia winked not telling him of a certain side effect to the modified spell.

Her ass jiggled again right before ballooning right before his eyes to the point where it covered the majority of his face. It was warm and soft underneath the princess's "pet". He was so happy to witness such a feat that he kept giving each cheek a sloppy wet kiss while massaging the other cheek, suddenly Tia's stomach rumbled again.

"Hey Discord."

"Yes my ass queen?"

"I'm hungry."

Author's Note

As always positive feedback is deeply appreciated and also let me know in the comments below which mare you want to see next. Favor and follow.