Late at night, you, the human, were sat in a purple leather armchair within a huge ass library inside a huge ass oak tree. Held in your hands was a newspaper. Yes, you were reading the news in a newspaper. Since the Internet, along with TVs were not a thing here. Thankfully, they had invented a lightbulb at least.
Unfortunately, there wasn’t any really exciting news in the newspaper to read. 90% of it was just ads trying to sell stuff. Thankfully, each one was basically a porno magazine as well. Each new weekly edition came with many pictures of plump pony butts. Without the drama you normally saw back home on Earth they were basically forced to sell porn to keep the paper selling. In particular, the pictures of Princess Celestia having sex with her royal guard and random lucky ponies made the paper fly off the shelves. Everypony, or everyhuman in your case wanted to read ‘The Plot Times’. That said, it seems you are the only human here.
You found yourself becoming semi-erect at the sight of Princess Celestia’s ass. Your cock in your shorts twitched at the sight of her. Celestia’s rump was presented on the entire page. Her right, bare hoof was pressed against her right buttcheek, creating a deep depression upon her sun cutie mark. You were tempted to masturbate, but you were in a public library, so you held yourself back.
Suddenly, you felt something soft, and spongy touching your left bare knee for a brief moment. You lowered the newspaper to see it was your good, cute little-unicorn friend Twilight Sparkle.
The little cute mare was sat down on her rump before you. Her big purple eyes did not meet yours, she was looking to the side while she fidgeted with her two, front hooves. Sweat poured down her forehead like a waterfall. She was blushing profusely in embarrassment.
She opened her mouth to speak, but no words came out. Whatever was wrong with her, it seemed she could not voice it. So with that, you reached down and took hold of her. Your right hand came to take hold of her cutie mark, while your left hand came to snake its way around her barrel and touch her stomach.
Twilight squealed in delight, which sounded like a dog's chew toy. Her big purple eyes literally sparkled in joy, and a big cheesy smile was upon her face. You felt a strange, tingling sensation happen to your cock and balls.
The softness of her warm fur against your bare skin felt wonderful. Your right hand sank deeply into her plush buttcheek.
So, with that, you hoisted the mare up onto your lap. Her rump came to rest directly upon your cock in your shorts. Your cock began to twitch from the sheer softness and warmth of her lovely, plump rump resting against it. Your member roared to life, gaining inches by the second. At the same time, your lap became damp with her warm marecum leaking out of her marehood. A strong musky scent filled the room as a result.
The mare stared at you with dreamy eyes, her lower lip quivering. She subsequently leaned forward with the intent of kissing you. However, you stopped her by placing your index finger upon her lips, mere inches away from reaching her destination. Twilight's eyes widened in alarm at this, and her mouth formed an 'O' shape.
"Twilight, I don't want to ruin our friendship. I think your heat is driving you crazy."
"Helping your friend during their estrus isn’t going to ruin our friendship. If anything, it will make it even stronger. Your penis will grow bigger if you help me in my time of need."
"I don’t care if my penis grows bigger, I don't want to take advantage of you. You are one of my only friends in this magical horse land. And…and " you were cut off when your cock tore through your shorts.
Twilight giggled with a hoof over her mouth. “Anon, you just empowered your penis even more with your kind words.”
You looked down in shock at the sheer size of your cock unleashed out of your shorts. Your member stood about 24 inches long and about 6 inches thick. Gravity soon took over, thus your heavy member came to land with a loud meaty slap against Twilight's rump.
"Uhh, Twilight. Why has my cock gotten so huge?"
"It's Friendship Fertilizer, a defensive magical spell inside all ponies. It's been with us even before we evolved sapience. In ages past, hungry predators would find themselves with a much smaller penis after killing and eating a pony. And if they continue to be aggressive towards ponies, their penis will shrivel up into almost nothing eventually. This will make it very difficult for them to pass on their genes as a consequence. However, if they befriend ponies they will be rewarded with having a much larger penis."
"That's a very unusual defense mechanism."
"Friendship Fertilizer is a necessary defense spell. Ponies are a prey species, thus most of us are not great warriors. The dragons could easily take over Equestria as they did in the past. However, since being cruel to a pony means your penis gets smaller, they soon pleaded to be forgiven to save their species from extinction.
"So, what happened?"
"Princess Celestia agreed to have pity sex with them and make their penises big again if they promised to not invade Equestria again. Their penises were made larger than they were previously before they attacked us."
“I suppose that makes sense. Anyone who’s mean to a pony deserves to have a far smaller penis as punishment,” when you finished saying those words, your cock twitched and gained several more inches in height. “Whoa.”
Your penis was now at least 30 inches long, and 7 inches thick.
“So, will you have sex with me?” she asked.
You rested your right hand on Twilight’s cheek and rubbed it affectionately. “Twilight, you’re my best friend. I don’t want to take advantage of you, even if my penis ends up getting smaller if your Friendship Fertilizer thinks I’m being somehow cruel to you.”
With that, your cock twitched again and gained an extra 10 inches… making your member, now 40 inches long, and about 10 inches thick.
“Uh… do penis shrinking spells exist. Because I think my penis will get out of control eventually,” you said in a worried tone.
“Yes. We can cast penis shrinking spells to stop a lover’s penis from going out of control. We however have pocket universes inside our mouths, assholes, and vaginas. So we can fit any penis inside us, no matter how big.”
Twilight’s horn became wrapped in a glowing aura of purple light. There then came a flash, and your cock was back to being 30 inches long, and 7 inches thick.
“Anon, if you are worried that somehow helping me in my heat will ruin our friendship. You can always just cuddle me.”
“Just friends cuddles? No funny business.”
“Of course. If I can’t have sex with you. Will you at least cuddle me?”
“Okay, Twilight. I will cuddle you.”
Sometime later. You and Twilight were in bed. Twilight rested her soft hooves on your chest, her head rested upon your shoulder. Your long, heavy cock rested between her plump buttcheeks. Your hands lay upon her lower back. The warmth and softness of her body against your bare skin quickly made you drift off to sleep.
Later. You awoke to a damp feeling on your shoulder. You heard quiet whimpering. Your morning wood (night wood in this case) stood tall and proud between her buttcheeks.
“Twilight?” you said softly.
Twilight lifted her head off your shoulder. You heart ached upon the sight of her being so upset. Her once beautiful, purple eyes were badly bloodshot. Rivers of tears were flowing down her cheeks, and her lower lip was quivering.
“Oh Anon, I’m sorry I woke you,” she said in a low voice.
“What’s wrong?”
“It’s my heat. It’s hurting me. But, I am willing to tolerate the pain for you. I don’t want to force you into anything you are uncomfortable with. You are my friend Anon. I will do anything for you.”
You sighed deeply. “I feel like a real bastard. Come mere, Twilight. I will make sweet love to you now with my big fat cock.”
Twilight squealed in delight, making a sound like a dog’s chew toy. Your cock twitched, growing in size by 10 inches, making it back to 40 inches long.
