Based on this pic: https://derpiboo.ru/163331
 
>You are a freshman at Canterlot high and the youngest member of the fashion club.
>(No you're not a fag, you just like dressing sharp.)
>Club is just wrapping up and most of the other members are leaving.
>All except two.
>Rarity and Fluttershy are junior girls and they run the club.
>For some reason they singled you out early on.
>Not that you mind.
>You constantly get to help two of the hottest girls in school.
>Although lately that 'help' has taken on a new dimension.
>Fluttershy carefully locks the classroom door and makes her way over to where you and Rarity are sitting.
>She grabs you gently by the shoulders and guides you off your seat onto the ground.
>Smiling at Rarity, who looks hesitant and expectant all at once, the taller girl sits down beside her companion and nudges her a little.
>They both look down to where you are sitting, your legs sprawled.
>Then they start to tease you.
>Their stocking clad legs extend until their feet make contact with your groin.
>They didn't even take their shoes off!
>But you totally go with it because you know that this strange duo has a secret.
>You have no idea how, but when they get aroused, their tits get bigger.
>The more turned on they are, the bigger their hooters swell.
>So you watch in fascination as they play their sick little games.
>You try not to get distracted by their feet rubbing your crotch, all the while watching as the normally quiet Fluttershy slips into 'dom' mode and Rarity tries not to reveal how much she loves these 'unladylike' trysts.
>As they continue, it's obvious neither of them have worn bras today.
>If they had, they would be in tremendous pain right now because their breasts are already tripled in size.
>Fluttershy's really getting into it now.
>You can see the majority of her tight cleavage through the diamond shaped gaps in her shirt - any bigger and cloth is going to start tearing.
>The pink haired girl normally has one of the biggest busts in the whole school anyway but right now they look like a pair of water balloons filled up bigger than her head, each boob jiggling and trembling with every motion.
>Not that Rarity's are bad either; what she lacks in size, she makes up for in shape.
>Each one of the prim girl's melons jut from her chest like they're straining to get away from her.
>They have a firm perkiness that belies their growing bulk; the fat, rounded cones thrust against her uniform.
>It's easy to see how worked up both of these strange hussies are, their nipples have enlarged right along with the rest of their knockers.
>Even if they were wearing bras you, their willing victim, are pretty sure their swollen nips would still be plainly visible, the hard points denting the fabric of their vests.
>Soon, what they're doing to you isn't enough to get them off.
>They each turn to the side and reach across to undo the other's top.
>Their feet are still rubbing your crotch, but it's a far more distracted operation as they lean into each other and start to make out.
>Hands move frantically as they try to undo strained buttons before it's too late.
>You grin as when you hear Rarity curse and the threads on Fluttershy's shirt tear.
>Soon, both top-heavy honeys are completely topless.
>Rarity is sucking on one of Fluttershy's bloated wobblers while at the same time pinching her friend's other rock hard nipple.
>Fluttershy, who looks like she's about to come undone, is mauling one of Rarity's boobs while she pants and moans.
>Both schoolgirls have a hand down the others panties and are fingering each other furiously.
>They've all but stopped their double footjob at this point, but you don't really care.
>You've undone your pants by this time and casually stroke yourself as the two sex goddesses above continue to frig one another, while their breasts grow and expand.
>Finally, about the time that Fluttershy's funbags get so big that they start to rest on her lap, her face tightens and she cries out.
>You can see glistening fluids trickling down the junior's thighs.
>Rarity slows down as her bosom buddy rides out her orgasm; it's just as well that she peaked, Fluttershy's titanic teats had grown so long and thick that it's doubtful Rarity would have been able to keep sucking on the one in her mouth much longer.
>Regaining her senses, the satisfied young woman looks to her friend and goes back to getting her off too.
>Fluttershy takes a page from her fashionista friend and hauls each of Rarity's watermelon sized boobs so they rest on top of her own massive mammaries.
>The purple haired girl's breasts are more elongated than spherical, though not really pendulous; it's as though some unnatural ligaments hold them up and allow them to project from her ribcage.
>Taking advantage of their incredible shape, Fluttershy begins to nuzzle the protruding pontoons, motorboating her pal, even as her soaked hand goes back to work beneath Rarity's skirt.
>You look on in amazement as Rarity's tits start to enlarge once again.
>You've never seen them this big before!
>Each scarlet nipple is at least and inch and a half long and as thick as a roll of quarters.
>Each throbbing gland pushes out at least two feet from her 6chest, though now they've stopped their forward growth and are instead fattening up, gaining in girth and fullness.
>By the time Fluttershy makes her final push, both girls are leaning away from each other because Rarity's gazongas have grown just as gargantuan as her gal-pal's!
>The pink-haired aggressor twists her head to the side and suddenly clamps down on one of her lover's distended teats.
>Like her own, the turgid tip is so wide that she can barely get her lips around it.
>Rarity's head suddenly falls back in open mouthed shock and she shudders in sweet release.
>As she silently screams, you can't help but feel that you've never seen her come so hard before.
>After a few moments, air fills the prissy girl's lungs and she gasps; all the while Fluttershy nibbles on her lover's thick nipple.
>When Rarity has composed herself, both over-endowed vixens drag their monster mams away from each other.
>It will take a little while before their bra-busting bazooms start to go back to normal.
>They both look down towards their pet club member and you can't help but smirk as you return their gaze.
>You're still rock hard, at some point the show above becoming so engrossing that you forgot to even keep stroking yourself.
>Fluttershy looks over at Rarity and giggles.
>"I knew we did a good job when we decided to keep him around."
>"Mmn..." Rarity agrees, "I know. So nice to have a capable assistant, isn't it?"
>The purple haired fashion major wraps her arms around her corpulent bosom.
>"And since we've got these glorious things for a little while more, it would be a shame to waste them, don't you think?"
>Fluttershy grins knowingly, "Why yes, Rarity, I do believe it would."
>She looks down at your crotch and licks her lips.
>"I do believe it would..."
 
>End