Race.

Harry noticed the envy in Luna's eyes as she watched Brownie's display of obedience and endurance. He knew just how much his little pony craved the thrill of competition. "Luna," Harry said with a mischievous grin, "It seems you're feeling a bit... left out. How about a little challenge?" He pulled out her bit so she can answer.

Her eyes widened in excitement, Luna nodded eagerly. "What kind of challenge, Harry?"

"A ponygirl race," he announced. "You and Brownie, both pulling the millstone. The first to reach fifty revolutions wins."

The buckskin ponygirl's ears perked up at the sound of Harry's voice. She felt a rush of excitement at the prospect of a challenge. The whip cracked once more across her ass, and she took off into a steady trot, pulling the millstone with surprising strength.

Luna watched for a moment before Harry whispered into her ear, "And the prize for the winner... a special treat from my wand. Think you can beat her?"

The silvery ponygirl's eyes sparkled with determination. "Oh, I'll beat her, Harry," she murmured, her voice filled with lustful anticipation.

With a flick of his wand, Harry conjured a similar set of bonds and harness for Luna. The leather and metal contraptions snapped into place around her body, and she felt the familiar tug of the reins at her nipples. She took a deep breath, mentally preparing herself for the race ahead.

The two ponygirls stood side by side, their bodies gleaming with sweat and anticipation. Harry raised his wand, and the crowd of spectators fell silent.

"Ready... Set... GO!" he shouted, and the whips cracked in unison, striking the flanks of both ponies.

Both ponies shot forward, their hooves echoing on the stone floor of the mill. The air was filled with the sound of their breathing, the jingle of their tack, and the occasional cry of pain or pleasure as the whips found their marks.

The race was tight, both ponies giving their all. The crowd watched, entranced, as the millstone grew blurry with their speed. It was clear that Harry's suggestion had been a stroke of genius. The competition was bringing out the best in both of them, pushing them to their limits.

As the two ponies approached the halfway mark, the whips grew more insistent, urging them to go faster. Luna felt the heat building in her loins, her dildos moving in and out with a rhythm that matched her stride. Each step brought her closer to victory, and with it, the sweet release she knew Harry's wand would provide.

Brownie's breathing grew heavier, her body straining under the weight of the harness and the millstone. But she had been trained to ignore pain, to push through it for the sake of her master's pleasure. And so, she pushed herself harder, her muscles burning, her mind focused solely on the task at hand.

The air grew thick with the scent of sweat and sex, the tension palpable as the two ponies raced towards the finish. The crowd held their collective breath, unsure who would emerge the victor.

And then, with a final surge of strength, Luna pulled ahead, the millstone spinning faster and faster as she approached fifty revolutions. The crowd erupted into cheers, and Harry stepped forward to award her with a gentle stroke of his wand.

The sensation was electric, shooting through her body and making her dildos pulse with pleasure. She felt her climax build, her legs trembling with the effort to keep moving.

But she didn't stop, not even when Harry called out, "Fifty!" She kept going, driven by the need to claim her prize.

The whips fell away, and both ponies came to a halt, their chests heaving. Harry stepped forward, a proud smile on his face, and Luna felt a sense of accomplishment that washed away any lingering doubt or jealousy she might have felt.

"Very good, girls," he praised, stroking both of their heads. "Luna, your reward."

He raised his wand, and a warm, pulsing sensation filled Luna's body, the dildos inside her growing even more intense. She threw her head back and let out a whinny of pure ecstasy as the orgasm washed over her, her legs quivering with the aftershocks.