"I suppose, but you have to promise me something." Mary asked the fairy.
"Anything, if it means I can finally belong!"
"Do faries grant wishes, like it says in the books?" She asked, mixing the dosage again. If her math was right, this should put the fairy to exactly 3 feet tall: a significant difference.
"No, we're not like that." She gave it some thought, her wings twitching behind her. "It's more like... Owing you a favor. Our 'Magic' you'd call it, takes care of the rest."
"I see. Well, here's your next dose-" Mary poured the dose into the sink nearby, making sure to plug it so the potion didn't drain. Hopping for joy, the fairy dove in, swimming a but around before she began to thrash about in ecstasy.
Her head emerged from the surface. "How long do you think it'll take this time?" She asked, looking down at her body. Around 5 minutes later, they were about to give up hope that the potions effects were still working, when suddenly:
"Oh!" The small sprite exclaimed. Getting up from her chair, Mary began to worry, when she finally saw what was wrong; Instead of steady growth, this time it happened in small bursts. "Nngh, this feels ama-zing. You need to try it!" She breathily exclaimed, climaxing as soon as the growth finished.
"Hmm, I just might..." Mary mused. Seeing her grow like this was turning her on more and more, maybe it wouldn't hurt if she joined in...