You the human, dressed in a fine, black tuxedo walked along a white marble hallway. You were flanked on both sides by two very large equines. Both of them possessed feathery wings upon their backs and long pike-like horns atop their heads. They didn't look like equines from your old world. For one thing, they had comically large eyes and had magically flowing manes, which blew in an unseen wind.

If you were to compare their size to anything they were basically elephants in the shape of horses. The dark blue one, on your left, stood at about ten feet tall or so. While the even larger alabaster one stood at about fifteen feet tall.

You became nervous at the size difference between you and them. You weren't sure this threesome with Princess Celestia and Princess Luna was a good idea anymore.

But then you remembered you were so desperate for sex that you will be willing to have sex with these giant ponies even if you couldn't adequately please them. Besides, it was they who asked you. They would have to be idiots to think you had a penis big and strong enough for them.

The three of you approached a large double golden door. Without a word, they magically opened the door. Your eyes widened at the sight of what seemed to be a white void within the door.

The two walked into the ‘room’, their hooves clopping lightly against the invisible floor. It sounded like stone, but there didn't seem to be a floor. Cautiously, you peered your head into the room, while still staying out of the room, your feet not touching the white ‘floor’.

You looked around the room to see nothing more, but more white emptiness.

“What is this place?” you asked.

Celestia leaned down to look at you at eye level, before speaking softly to you. “It’s a room we created for me and my sister to safely unleash the true power that’s inside us.”

“What true power?”

“This power.” replied Luna in a deep breathy voice, turning around in quick succession, and then she leaned forward to raise her massive ass high into the air before you.

Her cutie marks flashed with blinding light. She inched up higher and higher into the air by the second. You looked on in both fear and fascination as she grew in size before you. Her rump air ballooned outward, her legs below rapidly grew thicker and thicker to help support her rapidly-swelling rear end. Her hips truly became monstrously large, only growing bigger and bigger by the second – growing in size alongside her ass made her look absolutely breathtaking.

When Luna finally stopped growing, she had grown to be at least three times larger. She now stood at an imposing thirty feet tall. The cheeks of her rump were now like blimps.

“Is our rump to thy satisfaction for the moment?” she asked, staring back at you with bedroom eyes.

“Umm, Luna you're very pretty I’ll give you that. But how am I supposed to sexually please you?”

“Worry not little one. Thou shall sexually please us by being sat on by our royal posterior.”

Your eyes widen in alarm. “Ummm, I don’t want to be crushed to death.”

Celestia gasped in shock, her eyes narrowed into a hateful frown.

Luna's jaw dropped at what you just said. Her lower lip began to quiver, and tears began to form in her eyes. And she… even started to rapidly shrink down in size. In a manner of seconds, Luna became a mere four-foot-tall pony.

Being at such a reduced size seemed to have upset her even more. She uttered a loud wail of grief, and lay herself down on the floor and covered her face with her hooves. Whatever you did seemed to have hurt her feelings to the point it made her smaller.

“Don’t look at me! I’m so bony thin and small now!” she screamed.

“Anon, apologize to my sister immediately!” boomed Celestia.

Well, you were dead either way, so you might as well take your chances. You walked into the room and sat down in front of Luna.

“Luna---” you began softly.

“Don’t speak to us! Vile ape!” she boomed, looking up at you with a hateful glare.

You looked into her eyes, seeing how bloodshot they were and the look of hurt behind them.

“Please Luna, I’m really sorry. You scared me. I'm not some superpowered being like you. I am small, frail, and mortal.”

The mare crawled up to you and lay herself down on top of you. The look of hate in her eyes had vanished, replaced with a look of concern.

“We are sorry too Anon. We shouldn't have started our growth magic so strongly. We thought that thou would go insane with lust at the sight of our body augmenting in size. We are so used to seeing our Royal Guard bowing before us and worshiping our royal posterior, that we didn’t think thou would react any differently.”

“Your guards don’t fear you?”

“Of course not. Our bodies never harm the innocent, no matter how big they get. We even show mercy to the wicked. We facesit on them into submission until they change their wicked ways.”

“Are you sure this is not just going to motivate people to be evil If it gives them a chance to be facesitted on by you?”

“Somewhat yes. I know from experience.”

“You were once evil?” you asked.

“Yes, we were once Nightmare Moon. Thankfully, my sister saved me by facesitting on me until I turned back into Luna. Nightmare Moon could not stand against the power of our sister's rump.”

“How did you defeat Nightmare Moon with your butt?” you asked, turning to Celestia.

“We are the goddess of the sun, while our sister is the goddess of the moon. We naturally grow much faster than her, Plus, I used the power of the Elements of Harmony on my own backside, and my love for my sister only increased the strength of my growth rate.”

“Do you get jealous that your sister grows faster than you?” you said, turning to Luna.

“We are ashamed to admit it but yes. Part of the reason that we became Nightmare Moon was over our jealousy of our sister’s much greater growth rate than us.”

Tears began to fall down Luna’s cheeks, overwhelmed with emotion as she spoke in a soft voice. “My sister told me that her body could grow to consume the entire universe and beyond, but without the company of the Moon alongside it, it would lose its beauty. It was those words that defeated Nightmare Moon.”

“I love the story. But can I behold your glorious asses now?” you said, placing your hands on Luna’s buttcheeks. Your hands sank into her plush rear end, digging deeply into the squishy soft fat before meeting her strong muscles beneath.

“We shall try to ease thou into it this time.” she said in a hot breathy voice, looking down at you with lustful eyes.

Author's Note

I like to start off with a small quick read here before I add more. I don't care if this story sounds dumb, I want to write about growing giant pony asses.