Rarity can fuck herself... with his tool.

A few minutes later, they were upstairs in Rarity's luxurious four-poster bed. Isaac was laying on her carefully made bed, tangling up the sheets, like it was his bed to own. Rarity made a fuss about a lot of things, but when it came to materials, she knew her stuff and was willing to save up for the best. Her pillows were luxurious as Isaac arched his back and snuggled back into them, making sure they were digging deep into the curve of his neck for maximum comfort.

Rarity, meanwhile, was getting stretched out on Isaac's cock, moaning and whining in lust as his massive tool stretched out her needy pussy. "Nnnnnngh, Isaaa~aaac! Your cock... Haah... Your cock is conquering meee~eee!"

And what was Isaac doing to contribute to this mind-bending fuck?

Not a daaamn thing.

Using a combination of magic to keep herself steady and her own two luscious legs, Rarity was squatting down on his pillar and pushing herself up again, bending down deep to go all the way down his ridiculous length before ascending, coring out her poor equine pussy each time. She was literally doing all the work.

And from the sounds of her squeals and giggles and moans, she absolutely loved it.

"Aaahhhnnn! D-... Do you like the feeling of my pussy serving you, Master? B-Because it likes you! So, SOOO MUCH! GYAAAHHH!" Her pussy started clenching around his shaft, squirting juices that never seemed to end. "My King! My God! My everything! You! Are! The Master of my pleasure! You're not even doing anything and it's driving me to escstasyyyyyyyyy!!" Rarity's voice screeched as her rapid-fire orgasms reached a crescendo that made her whole body convulse and tense up. The only thing keeping her upright in that moment was the massive human cock spearing her pussy and bulging all the way up to her ribs.

Hearing her drive herself to orgasm while squeezing his cock like she was trying to milk it dry? Yeah, that was plenty enough to draw an orgasm out of Isaac. His cock pulsed inside her, dumping pint after pint of human seed into her stretched-out womb, her belly puffing out like it was trying to compete with the other globes of her hourglass figure.

Still twitching in afterglow, Rarity moaned and placed a delicate hand as she felt her abdomen fill with sloshing semen. "S-So warm... so thick... D-Do you happen to know if, erm, humans and ponies are compatible...?"

Isaac shuddered as his orgasm started to slow down, though the question gave him pause. Long story short, he definitely didn't even want to entertain the thought of having offspring. "Didn't Twilight at some point determine conclusively that while sex between our two species is perfectly safe, there's zero chance of procreation?"

"Ah, y-yes, now I remember. She ran some tests or something..." Rarity murmured. It was hard to tell whether she was disappointed in the answer or not. Maybe she didn't even know herself. She shuddered again as one last big load of semen rounded out her abdomen. "Mmmf. I've got many career-minded years ahead of me, so I'm glad... but even if this reckless romp had resulted in some little Isaaclings, I want you to know that I would have dropped everything for them in a heartbeat."

It was a sweet gesture, but thankfully meaningless, and Isaac just had to chuckle. "First off, mm, never say 'Isaaclings' ever again. Second, breeding is actually kind of a turn-off for me due to some past life experiences. Feel free to spread that bit of gossip around."

"I-I see..." Rarity then leaned forward, toppling breasts and belly first onto Isaac's body. His cock was still inside her, so it got tugged upwards by her still tightly gripping pussy. Her breasts smooshed against his shoulders, and she planted a weary but passionate kiss on his lips. "Mah! Well, perhaps you should see if the Princesses are willing to share the secrets of immortality someday. One way or another, we'd all like to have some form of continuity and legacy with our beloved Harem Master."

Now there was an idea. Living forever, fucking generations of ponies throughout the ages, guiding their culture into more advanced versions of his lewd, self-serving paradise...

Isaac's brain usually liked to mine such rich ideas for possible scenarios, but just this once, he let it all slide, deciding not to worry about it right now. The fact that his future was full of such wonderful possibilities was the blessing, whether they were realized sooner or later.

Right now, he had a well-fucked Rarity in his arms, and he hadn't even needed to lift a finger. Life was very, very good.