Mighty Macintosh
Luna was visiting Sweet Apple Acres after placing an order for a dozen famous Apple family pies for her dear sister.
"Here ya are, one dozen pipin' hot apple pies." Applejack said placing the tray of pies into individual boxes for the lunar Princess.
"Thank you very much fair Applejack. Twilight was correct, you always do come through." Luna said accepting the dozen boxes using her magical horn to levitate them all.
"Think nothin' of it. Ah just had a bit of spare time after helpin' Big Mac buck a few trees is all."
On cue the giant red stallion walked into view holding two twin barrels of apples above both his shoulders.
"My my, your older sibling sure is strong."
"Yessiree, he's PonyVille's strongest stallion. Shucks maybe even all of Equestria."
Luna was giggling softly a bit holding back her laugh.
"What's so funny?" The apple farmer said raising an eyebrow.
"Oh nothing, nothing. I just find it amusing is all, Big Macintosh here does have a fairly....how you say "buff" physique but he pales in comparison to a champion weight lifter back in my day."
"Really? Who is he?"
"None other than Steel Beam the strong who lived during the early Canterlot years. He served as the trusty castle blacksmith creating the very armor, weapons, and railroads we use till this day and he did it all with his bare hands. No one was stronger than him."
"With all do respect, ah must say ah disagree with that. Big Macintosh is the strongest stallion alive and he could 'ave done all those things just as good. Shoot, maybe even 10x better even."
"I admire your faith in your kin but Steel Beam was a god amongst normal earth ponies, he was ahead of his own time yet lived almost a quarter of Celestia's lifespan. And in honor of his life I bestowed upon his grave the title of Equestria's strongest stallion that ever lived."
"Well that title should belong to Big Mac now, no matter what the challenge is."
"Oh? Care for a friendly wager then?"
"What kind of wager?"
"Fairly simple one actually. If you are so confident in your brother's ability then an actual demonstration is more thann necessary."
"...I'm listen'n."
"One week from now I will choose the heaviest thing in the Canterlot castle for him to lift. If, and only if he succeedes in doing so I will bestow upon him the title of the strongest stallion alive."
"Okay, but let's make it a bit more interestin'n."
"Hmm?"
"If Big Macintosh wins...you would have to strip naked...in public."
Luna's face blushed wildly after hearing that.
"I think we have ourselves a bet." She said extending her hand.
"Ah believe we certainly do." Applejack said accepting the gesture.
Luna soon left afterwards leaving Applejack to focus on making sure Big Macintosh is in proper shape for the bet. Cue weight lifting montage! As for Luna she headed back to her castle in Canterlot with the must sought after pies Celestia requested for, she was glad to see her little sisteis eenter her private chambers. Luna sneaked a quick peek at her sister's backside, to her it was probably weightless to the princess of the sun but to a mere mortal like Macintosh he wouldn't be able to withstand the weight of a thousand suns on his shoulders. It was perfect.
"Tia, in return for doing this errand for you how about you help me settle a bet?"
"Well, that depends. What's the bet exactly?"
"Nothing major, just a small test to see if Big Macintosh of the Apple family is worthy of the title of Equestria's strongest stallion alive. And to do that I must select the heaviest object in the Canterlot castle."
"Oh, so what did you have in mind?"
"Well what better choice than the biggest and most beloved treasure of the princess of the sun?"
"I don't follow."
"Your flank dear sister."
"Luna!" Celestia exclaimed blushing a bit.
Lately she has been rather self conscious of her ever growing backside, even the slightest comment about it embarrasses her.
"No need to feel embarrassed dear sister, everypony in Equestria adores your large jiggly backside. It's without a doubt the crown jewel of the entire nation."
"....It is?" She sniffed.
"Of course, it's more valuable than all the diamond mines in the world. Steel Beam was honored to even craft your beloved throne to your liking, won't you honor his legacy?"
"I...suppose. So what would I have to do exactly?"
"Nothing really for the moment. There's no way a mortal can lift such a bountiful booty like yours."
"Why thank you Luna....I think."
Luna thought about it for a moment, the citizens of PonyVille have completed countless feats before and a large red stallion was no different. Celestia's booty was big, question is was it big enough?
"Sister, how about you have another pie?" She said levitating another pie closer to her sister.
"Oh, don't mind if I do then." Celestia said readying herself for another helping of mouth watering delight.
Meanwhile Luna poked her head out from the private study's entrance catching a royal guard patrolling the hallway.
"Excuse me, would you mind informing the chef to prepare a few desserts for us?"
"Of course Princess, right away Princess." The guard said bowing before quickly rushing towards the kitchen.
Shortly after there was a knock at the door, Luna answered to meet two maids carrying several trays of delicious looking dessert cuisines. She accepted the trays and thanked them before returning to her sister who had already finished the rest of the pies and starting to feel quite full already.
"I hope you saved room."
"Actually, I don't think I can eat another bite."
"Well we can't have that now can we?"
"What do you mean?"
Luna said nothing, she was already charging up her horn preparing a spell.
"Luna?"
The moon Princess fired hitting her sister with the hunger enhancement spell, immediately Celestia's appetite returned ten fold feeling as if she hadn't eaten for almost a year. She dove into the sweet delicacies swallowing practically everything whole, minutes later her belly started to expand rounding out underneath her dress her dress making her feel uncomfortable. She quickly resolved that problem by stripping bare naked, Luna was eyeing her bouncing back side waiting patiently for it to get as big as she needed it to be. Of course, why wait? While her sister continued to indulge in the fattening sweets Luna crept close behind with her horn glowing preparing to unleash another spell, the double-up spell doubling the production of fat cells in a specific area as a dark blue aura surrounded Celestia's plump booty.
Slowly but surely the sun princess's plus sized backside was slowly doubling in size shaking and jiggling with ripples as more and more layers of fat piled on and was disputed evenly in her meaty cheeks, hips, and thighs making her even more bottom heavy than before. Luna was gently massaging each soft squishy cheek as the growing mass showed no signs of stopping soon. Celestia had finished the tray of desserts sighing in content before looking back at her enormous luscious new booty nearly triple the size before bouncing up and down making loud sloshing sounds with every small movement she made.
"Luna! I'm huge!" She cried out in surprise once the hunger had subsided.
"Not big enough dear sister, not big enough." Luna said with a creepy smile as her horn lit up again.
One week later everypony was surrounding Canterlot square anticipating the grand event, Applejack stood close to Big Macintosh who after an entire of intense training and encouraging motivation from his two sisters and the citizens of PonyVille was more than eager to show his worth. The onlooking crowd slowly opened up forming a path as a large figure came forward, Big Macintosh's jaw literally dropped to the ground as Celestia herself came walking towards him standing three times her already incredible height with a large plump jiggly ass so big that words could not justify. Luna appeared right next to Applejack with a smug looking grin on her face.
"So....still think Big Macintosh stands a chance?"
"Ah-Ah, H-How did the princess get so *gulp* big?"
"I'd bore you with the details but I think we better let the princess take her seat. Isn't that right dear sister?"
"Quite right Luna, problem is however...I don't see any chairs available." The supersized princess said looking around.
"Why of course you do, he's standing right here."
Luna gestured to Big Mac, Celestia understood. She slowly turned around facing her her planet of an ass towards him, the big red stallion started shaking a bit in intimidation.
"Big Mac! Just remember what we practiced!" Applejack called out reassuring her older brother.
"You ready?" Celestia teased shaking her ass a bit letting it jiggle a bit.
"Eeeyup." Big Mac announced positioning himself underneath her.
Celestia slowly lowered her bountiful booty on top of the stallion wide open palms, immediately his hands started to slowly sink engulfing his hands up to his arms like quicksand with no signs of stopping. He struggled to find a point of leverage but was sinking inside way too fast, soon he would be sucked completely inside Celestia's ass. Things were not looking good as Big Macintosh started to loose vision as his upper body was sinking inside.
"Big Mac!" Applejack cried out as the last of her brother disappeared underneath Celestia's ass.
All was silent except for Luna who was snickering a bit feeling content that she had won the bet when suddenly Celestia started to slowly rise from the ground, the crowd cheered as Big Mac appeared again heaving the national treasure of Equestria high above his head. Luna stared in complete shock and disbelief as a mortal was actually able to lift the sun. She soon felt a cold shiver run down her spine as Applejack looked with a smug look of her own.
"What?"
"Oh nothin', just that y'all now have to hold up y'all's half of the bargain."
"Oh no."
The next day:
Luna was true to her word and appeared in the center of PonyVille as a crowd of more than eager male stallions stood at attention, the lunar princess sighed heavily swallowing her pride and getting the punishment over with. Dressed in only a night robe she unfastened the string like sash around her waist allowing the robe to fall off her naked body, the stallions whooped and cheered taking pictures of the glorious sight as Applejack and Big Macintosh stood in the crowd laughing aloud in victory. Luna was blushing red but was able to look up at the two.
"D....Double or nothing."