I backed away from my sister, trying to explain I was just curious if she had to power to turn someone into a frog. I didn't actually want to be one!
For every step I took back, she took one forward, smiling coyly. "I transformed you into a girl for leaving the toilet seat up, so I expected you to be upset, but instead you asked if I could turn you into a female frog. I never knew you were so kinky, brother. It works out well, though. I love slowly transforming people and you like being turned into things. This will work out for both of us."
I shook my head as I croaked, "Ribbit! ribbit!" I didn't want to be transformed into a frog, much less a female! Bumping into something, I turned to see the wall behind me. I had nowhere to go. My sister's smile grew as she continued forward. She planted both of her arms against the wall, blocking me in. I hadn't realized she was now bigger than I was, now that I was a girl. Her heavy breathing indicated she was getting turned on by my predicament.
"Even though it's cliche', I really love a good frog transformation. The sleek, slick green body, long slimy tongue, and those slender legs," my sister said as she leaned in and whispered in my ear. "I find it sexy."
"Ribb-" I began to protest, but she leaned in and kissed me hard on the mouth. "Mphmph!" I stammered as her tongue wormed its way between my plush feminine lips. She grabbed my wrists and pinned me against the wall as her tongue flailed against mine. At first I was shocked, but I soon succumbed to my sister's will and began return her french kiss, my tongue entering her mouth. After a few minutes, she pulled back, smiling. My tongue was still wrapped around her tongue, except mine was now a long frog's tongue. It whipped back into my mouth. My sister wiped her hand across her sleeve and smiled. "See what I mean?"
The moment of lust now over, the fear of being transformed into a frog now resurfaced. I looked up at her hands holding mine and realized my hands now had only four webbed fingers. "Ribbit!" I protested as I struggled against my sister's firm grasp. Not only was I smaller than her as a girl, but I was much weaker.
"Oh, your first transformation can be quite jarring, but you'll get used to it," she said as she looked me up and down. "There. Those are those sexy female frog legs I love to see," she said as she nodded down. I followed her gaze to find my legs were now slimmer and had turned a light shade of green. My feet now resembled my froggy hands. She moved one of my hands toward the other and held them both in her firm grip. I struggled against her, but couldn't break free. With her free hand, she traced her fingers up and down my upper thighs, apparently fascinated by my new legs. She reached up and began fondling one of her breasts and closed her eyes, moaning.
I watched her as she fondled herself, her hand then slipping down into her panties. I could see her fingers moving up and down. I felt my own body grow flush as I watched my sister masturbate. She opened her eyes and looked me over. "Getting there. Do you know how this spell works? The more you're turned on, the more you transform. If you weren't horny right now, you'd still be human. But you're getting a kick out of me slowly molding you into a frog, aren't you? Or maybe you just like watching your sister pleasure herself? You're a twisted boy, either way. Or at least you used to be." She leaned in close again, "And you know what? I like it. You're twisted like I am. Why don't we just finished this up? I can always transform you into something else later. A sow, maybe? A pair of my panties? Well, there's the rest of our lives for that. For now, I want to see your sexy body hopping and croaking helplessly. Now...how to turn you on even more?"
Her gaze fell onto my chest. Lifting up my pajama shirt, she began rubbing my petite breast with her hand. She looked me in the eyes and smiled as she leaned in and began tracing her tongue over my nipple, sucking and teasing it for minutes. "Don't worry, I'll let you keep these," she said breathlessly as she continued to caress and lick my breasts. I could feel the heat from my groin growing as I whimpered. "R-ribbit!" I said weakly.
She looked up and smiled. "You're such a little froggy slut, aren't you? Just my kind of girl. Oh...what's going on down here? Your panties are soaked, brother! They'll just have to go." She partially pulled down my plain pink panties with her free hand before using her foot to slide them down to my feet. I looked down at my smooth green belly and groin, but unlike when I was a boy, I couldn't see anything there.
My sister chuckled. "Why, I'm not sure I've ever seen a blushing pink and green pussy!" she said as peered at my exposed sex. I felt my cheeks inflame in embarrassment. She stared me in the eyes and gave a wicked smile as she moved closer and once again forced her kiss on me. I jumped as I felt my pussy penetrated by her fingers at the same moment. I wanted to cry out, but her mouth over mine prevented it. Her fingers and tongue invaded my body, sliding in and out slowly. I moaned at the pleasure. I'd never even kissed a girl before, so the experience was overwhelming. She began thrusting her fingers in faster and faster. The world around me spun as I felt as if I were going to burst. My body shuddered as it felt like my new pussy was pulsing and burning. My sister stepped back, a trail of slimy saliva connecting our mouths. "Did you just cum?" She looked down and then laughed before looking at her two fingers, which were covered in my fluids.
"You did! Congratulations on your first female orgasm, brother. And it looks like my work here is done," she said as she let go. I fell to the floor, still shaking from what she'd done to me. I felt so weak and helpless, as if I could barely move. After a moment, I tried to rise, but found I couldn't. For some reason my arms wouldn't push up like I thought they should. I looked down and found my arms were now green and thinner, ending in frog hands. "Ribbit?" I said as I looked down at my legs folded underneath me. They were nothing but frog legs now, unsuitable for walking. My skin was now a dark green shade, and reflected the light. Once again, I tried to push myself up or stand, using all my strength. Instead, I leapt forward, settling down to the ground two feet away. My sister's laughing erupted from behind me. I turned to see her looking down, amusement on her face.
"Oh, that's what I wanted to see. You turned out to be a very sexy frog, brother!" She materialized a mirror in front of me. I was shocked to see my body almost completely that of a frog's except I retained my small breasts and visible pussy. My face was that of a frog's as well as my eyes. My long hair was gone. I was also still human-sized, not shrunken down to the size of a normal frog.
"R-Ribbit! Ribbit!" I protested as the mirror disappeared.
She smirked as she cocked her head to the side. "I've got to go, but I had a lot of fun. You wait here for me and I'll return you back to normal size once I get back." She snapped her fingers and suddenly I couldn't move or speak.
She leaned down and kissed me on the mouth. "Don't worry, no one's kiss will return you to normal. Only I can do that...sister."
I struggled to move but could only watch as she got dressed and left, locking the door behind her.