Softly rubbing her cunt through her bathing suit quickly made Luna even more aroused. Her moans grow in volume and her hand moves to your pants. You push her bathing suit aside and start rubbing her wet pussy while she pulls down your pants with a sharp tug. She stares at your decently sized dick and impressive sac before undoing the knot on her top and letting her firm breasts free. She strokes your dick slightly and looks into your eyes, her gaze telling you what she wants.
The others still watching, you pull off the bottom of her bathing suit and get between her toned legs. With a look down at her wanting gaze, you slide your full length inside her, earning a long and lusty moan from the princess. You can feel her pussy gripping your cock very tight and pulsing around your shaft. You start thrusting slowly, the head of your dick touching her cervix with each thrust.
Princess Celestia still watched, her own wetness practically soaking her bathing suit and running down her thighs as your thick cock penetrated her sister again and again. Cadence was rubbing one of her breasts with her hand, blushing deeply and very aroused at the sight. Chrysalis, having cum from hearing Luna's loud moan, now watched while her pussy gushed with wetness.
Luna cums before you, crying out loudly and growing even tighter. Her pleasure was so intense that she actually squirts around your shaft. Your moment of pride at making a Princess squirt was quickly overridden by your own impending orgasm. <Cum on me> she whispers into your mind <release yourself onto me>
With a loud grunt, you pull out and spurt a hot load onto Luna, your hot spunk hitting her toned stomach and her breasts. Luna moans loudly at the feeling, clearly enjoying it. Once you finish spurting, however, you quickly feel another surge coming from your nuts. Without thinking, you suddenly plunge your dick back into Luna's tight, wet hole. The Princess cries out in surprise when you shove all the way inside her again and quickly realizes what is about to happen. "No!" she says, an edge of panic in her voice. "You can't cum inside of me! Pull out!"
It's too late to pull out and you cum inside her. The surge of cum after your first load is enormous. A huge amount of hot and obscenely thick spunk erupts from your cock and, as your head is touching her cervix, blasts straight into her womb. Your immense load quickly fills Luna's womb as she can't help but scream in pleasure as she orgasms from the sensation. Your load fills her womb completely and then fills her pussy up so quickly that it starts squirting out of her around your cock and onto the towel behind you. You groan loudly, the pleasure making you a bit dizzy as your throbbing cock keeps pumping the huge load into Luna and squirting the excess out.
Cadence and Celestia had both nearly reached orgasm when you shot your load onto Luna. They both really came when you shoved your dick back into Luna and started cumming inside her. Both princesses reached squirting orgasms, completely soaking the bottoms of their bathing suits. Chrystalis had started fingering herself again and had cum as well.
You finally stop cumming and breath heavily. The excess cum had gotten on both your thighs and hers, not to mention the towel. With a low sigh, you slowly pull your still-erect cock from Luna's pussy, releasing a stream of your cum to gush out of it. Luna was panting as well, moaning lowly as your cum leaking out of her pussy and down her ass.
Once everything had calmed down a bit...