Fluttershy grows from having sex. Anon and her get frisky?

“Ooh. Ooh. Right there. Oh!”

Anon grunted as he thrust up into Fluttershy, his dick harder than it’d ever been. Fluttershy, for her part, seemed to be more than enjoying herself. As for Anon, each thrust, each smack of Fluttershy’s body against his felt incredible.

His hands roved hungrily over her stomach, pulling her closer to his chest and pinching and teasing as she moaned. He nipped her ear, then her shoulder, and her whole body shuddered.

At first, he didn’t even notice that she’d gotten bigger. Ponies, while little, were heavy enough that a few pounds difference wasn’t enough to really notice. But within a few moments, that few pounds had grown into a few dozen, and a few centimeters into inches.

“Mmff,” Anon grunted. “Fluttershy, you’re…”

“Oh!” Fluttershy’s moans cut off. She looked down at herself, still impaled on Anon’s dick, and flushed. “Oh, my. I /am/ growing. I’m sorry.”

“Don’t be.” Anon stared as Fluttershy’s rear, which had previously been able to fit neatly on his lap, began to overflow. “It’s amazing.”

“But - “

Anon leaned over Fluttershy’s shoulder and kissed her, long and hard. Her mouth was bigger, and her grip on him seemed stronger as she tasted him. “Keep growing,” he growled playfully once she pulled back. “For me?”

She looked abashed for a moment. “Are you sure?”

“It’s the hottest thing I’ve ever seen.”

“Really?” Fluttershy asked timidly. “Then what about - “

She pivoted on her side and pushed him to the mattress, her entire body pinning him down. One oversized hoof traced down his chest. She leaned over and breathed softly on his face.

“ - this?”

Anon moaned as Fluttershy rode him, her whole body grinding and twisting on his dick. His hands slid up and down her hips as she moaned in return, even when her hips began growing and her head began stretching above his. First an inch, then two, then a half a foot. And still, he fucked her, sweat streaming down his face as he watched her slowly tower above him.

“Mmff,” Fluttershy moaned, her growth petering out for a moment. By this time, she’d have been a full foot taller than Anon had she been standing on four legs; as it was, just looking up at her, it seemed like he was fucking Celestia herself. She leaned over and slowly brushed her lips over his - well, face. He savored the feeling of his mouth on his and held her head close.

“You’re so big,” he moaned as she nuzzled him.

“Mm,” she murmured, gently pushing his hair out of his eyes. “Not big enough.”