You were now situated within a gym, various gym equipment was spread throughout the room, such as; treadmills, stationary bikes, rowing machines, and weight benches, and simple benches.

Unlike back home on Earth, they literally had weights that were made from the same material from a neutron star, although they were not blindingly bright. If somepony found those too light there were literally weights that were called 'alicorn weights'.

You were sat on a wooden bench. Before you stood the imposing figure of Fluttershy. Her massive body loomed over you. She stood at around ten to fifteen feet tall or so. She was of a more slender build when compared to Applejack. Nonetheless, her legs were still quite thick. Her hips were still wide enough you would only be able to touch one of them at a time.

The size of Fluttershy's breasts however were much bigger. Easily twice the size that of Applejack's beach ball like breasts.

Fluttershy made to turn around, her hooves clopping hard upon the stone floor as she did so. You were now given a good look at her absolutely huge backside. Each cheek of her ass was like that of a bean bag…. a really…. really big bean bag. They were thick and bubbly, and perfectly round. Not soggy in the least. It was as if her ass was carved by the heavens themselves. Her large, pink tail only made her ass even more beautiful. Big as Fluttershy’s ass was, Twilight’s ass was even more monstrously large.

"Has my unbreakable vow been reset?" you asked.

"Yes. You have not broken the vow in any way. Your vow timer has been locked and reset the moment you entered this gym. I will warm you if you break the vow at any point." said Twilight, standing before Fluttershy.

“Oh, that’s a relief.” your body suddenly became encased in a purple glow for a brief moment. “What spell are you casting on me?”

“An auto-healing combined with an auto-resurrection spell to stop you from dying during your workout.” said Twilight.

"Can you add a pain nullifier?"

"No pain, no gain. I'm sorry, but it is the only way." she spoke softly, looking down at you with a sad, sympathetic expression.

You gulped in fear. “Can we… at least do a gentle warm-up before we begin?” you said in a low, nervous voice.

Without a word, Fluttershy turned around to face you.

“I’m going to pick you up. Okay, Anon?” she spoke softly, much softer than all the other ponies you knew so far.

“Yes. Fluttershy, you can pick me up.”

“I need you to strip naked Anon before we begin.”

You quickly took off your clothes. But you found yourself hesitating when you were down to just your underpants. Your erection poked through your underwear.

“Don’t be shy Anon. Strip down. You don’t want to break your vow.” said Fluttershy softly.

Reluctantly you pulled down your underwear to reveal your penis to the massive horsewoman. You were embarrassed and blushed hard as you felt weak and exposed.

“Don’t feel ashamed Anon.” she said softly.

She leaned forward, bringing her double beach ball massive breasts closer to your face in the process, they cast a dark shadow as they loomed over you. She moved her right hand from underneath you, she gently took grip around your butt. She placed her other hand on your upper back. Now with both hands, she lifted you up and cradled you in her arms like a baby.

"Uh, Fluttershy? How are you not breaking my bones?"

“I am able to suppress my strength. Not many ponies can do that.” she spoke softly, before pushing your body into her soft, right breast. “Drink up, Anon. You need your strength.”

Your body sank into the soft, malleable flesh of her breast. You shuddered at the great softness and warmth of her breast pushing against your body. Your cock poked hard against her soft breast. Her soft fur against your bare skin made things only even better.

You opened your mouth wide and took her fat, bloated nipple into your mouth. You looked up nervously at Fluttershy as your teeth rested gently on her nipple.

“Don’t be afraid to bite down hard on my nipple. You can't physically hurt me. For example, I can lift entire neutron stars with my bare hands. I went for a swim within the core of a hypergiant star before. I even use a black hole’s gravity to give myself a massage on a daily basis.”

You pulled your mouth away from her nipple. “You can survive being in the presence of a black hole? Just how strong are you ponies?”

“Very… very strong. Now drink up, Anon. You need your strength.”

Without a word, you latched on hard onto her nipple, and you subsequently began to suck on her nipple with force. Fluttershy cried out a throaty moan, as thick, creamy milk spewed from her nipple into your mouth.

You moaned heartily into her breast as her milk flooded into you. Her milk was sweet and creamy to the taste with a hint of vanilla. A powerful tingling sensation coursed through your entire body as you drank down her milk. The sensation ran through your body as you felt slightly painful electric shocks flow through it, starting from the top of your head to the tips of your toes as the waves washed over you.

Your heart was pounding in your chest. Your muscles were contracting painfully and you were sweating profusely. You took deep breaths through your nose as you continued to drink down her delicious milk.

You could not help but grind your cock against her soft breast. True to Applejack's word, you felt your cock growing larger. Your member grew inch by inch from each passing second, depressing deeper and deeper into Fluttershy's soft breast. Your balls became heavy underneath you as they too grew in size.

You uttered a muffled scream of pleasure around her fat nipple, which made her giggle happily. You thrust your cock back and forth against her soft titty flesh, uttering muffled moans and groans as you did so.

Many sounds filled the room. The sounds of you sucking upon her nipple with throaty moans, while she in turn moaned herself. There were the loud sound of slapping against flesh as you slammed your growing balls against her tit. Your balls were now currently the size of grapefruit and still growing.

With a loving hand, you caressed the side of her huge breast. Like soft dough, your hand sank into her plush flesh. You subsequently pulled your hand away and watched in amazement as it returned to a perfectly smooth shape.

You brought your hand back down again and lovingly rubbed the soft flesh between your fingers. Fluttershy cried out in bliss as you massaged her breast.

Abruptly, Fluttershy pulled away when your cock reached about fifteen inches long and slightly thicker than your own upper leg. You now had a pair of balls the size of coconuts underneath you. Your cock defied gravity and did not bend down in the slightest as it stuck out from your body.

“That will do for the moment.”

“Does your milk keep growing cocks bigger and bigger?” you asked.

“Yes. But we can fix that issue with penis shrinking spells if necessary. Now let’s move to phase two of your warm-up.”

Fluttershy lifted you up further to her face. She opened her mouth wide and brought you closer and closer to her mouth. Her warm breath bombarded you as your cock came into her mouth. Her breath smelled minty fresh, so there was no real issue at all.

Gently she closed her mouth. Her huge, plump lips came to encase the base of your member. Your balls touched against her plump, wet lips. Your face rested against her lower snout and your feet were touching her chin.

Your body was shaking uncontrollably. Your eyes came to a close as you sighed in pure bliss. You uttered a loud moan when her soft, wet tongue came to wrap itself around your member.

With a powerful tug of force from her hands, she used her hands to move you back and forth as she pushed you against her face. Your long, thick cock rubbed against her soft lips, along with an absolutely wonderful sensation of her incredibly soft tongue touching off your member each time your cock was brought back into her mouth.

Loud slurping could be heard as she sucked you off vigorously. You cried out in absolute pleasure as your legs weekly kicked her chin. Great warmth and softness encased your member within her loving, wet mouth. Your cock was moist and slick with her saliva.

You were a quivering mess within her hands. Your whole body was shaking uncontrollably and you were sweating profusely. Your heart was beating in your chest. A tingling sensation was coursing through your cock as you found yourself at near release already.

"Cum for Mama Fluttershy." she spoke telepathically in your head.

As if by her command you subsequently released into her. You screamed as you released glob after glob of your creamy human spunk into her mouth.

Fluttershy cried out as she grew violently in size. Your cock slipped out of her mouth from her massive growth spurt. Your entire body became encased within her titaness hands, drowning out the light. You heard the sound of Twilight screaming as well as the sounds of destruction.

"Oh my." Fluttershy simply said.

She opened her hands. Above you stood a skyscraper tall Fluttershy. Her breasts were so large that you could not even see her face. Her boobs were basically like football stadiums.

"Let me fix this." said Fluttershy.

Fluttershy snapped her fingers and she was back to... normal size. You were returned to the gym as if nothing happened. Except for the fact that Fluttershy was now an alicorn.

Twilight gasped in shock. “This seems more complicated than anticipated. Your cum seems to have made Fluttershy... stronger... I can't even read her power level it’s off the charts. Even beyond Celestia and Luna combined. Fluttershy, you are the single most powerful being in known existence at the moment.”

“Oh my. I wonder if Anon can handle my ass now?” said Fluttershy, blushing in embarrassment.

“Fluttershy, I made an unbreakable vow. Even if you kill me you can bring me back to life.” you said with patriotic vigor while giving her a salute.

“Okay Anon. This is going to hurt… a lot. Even now, at a reduced size I feel a lot heavier before I became an alicorn.”

Fluttershy lifted you up to her face and gave you a simple, soft kiss on your lips… entire face. She gave you a warm smile before she gently placed you down on a black gym mat upon your back.

She turned around and showed you her massive backside, casting a dark shadow as it loomed over you.

“My body is ready.” you said in a low, nervous voice.

Author's Note

I probably released this too fast. But I felt like I want to show it anyway.