"what's up big bro, why don't you play with your little sis, or should I say little pussy~" melanie giggled again while jeff tried to not moan feeling his vaginal walls twitch every time she spoke. "No way I'll follow your mad ideas, I have enough with having a pussy, and much worse, YOU being that pussy" he answered.
"Booo, what a party pooper, you were always the boring sibling" she said, "like you were any funny, this isn't a prank anymore, this is a torture for me!!" Jeff yelled at his still naked crotch having melanie attached, as a small bulge functioning as a vagina. "Precisely!" the pussy sister smiled, "just because you're not enjoying it doesn't mean that I'm not, and since you don't want to play with me I have better plans for you~"
Jeff started to feel weird as if having his sister as a feminine sex organ wasn't enough, he realised that he began to lose control over his legs, the feeling expanded to his waist, torso, arms and neck in that order, he felt like he was paralyzed, just being able to rotate his head and even that was really limited. He thought he was completely frozen until his left arm raised itself, "what the-" Jeff heard Melanie's annoying laugh again, "IS THIS DONE BY YOU TOO!?" He screamed. "Correct! How smart you are big bro~" Melanie teased Jeff and was patted on the head by his own hand. "But how!? You're just a pussy!!" he asked, Melanie explained, she was absorbed by her brother's body of course at her will and merged with his internal anatomy, just the vaginal part, but also was connected to his nervous system, she decided to expand herself and merge with Jeff's nervous connections, taking total control over him.
"You should have paid attention to biology class, the one you said many times that didn't deserve your attention now is against you!" Melanie said, jeff struggled but only his head was able to move. "Now I'll give us a real sibling quality time~" Melanie perfectly controlled Jeff's body as she could change her point of view to Jeff's eyes to not obligate herself to just look through her lower sight as a vagina. Then they walked to Melanie's room, opening a drawer with a key showing many sex toys.
"Do you have sex toys, and many of them!? Does mom and dad know about this?" Jeff asked. "No, and they will never know hehe" Melanie answered. "I will tell them and I'll erase their perspective towards you as their supposed innocent and cute daughter!!" Jeff yelled. Melanie smiled and laughed again, "well, maybe you're kinda funny!" She kept laughing, "should I remember you that now I have complete control over your anatomy? I could make you leave every time you wanted to say a thing to them, or I could control your mouth to say anything else, hell, I could even take your life or change yourself and feel how you struggle!" She evily laughed, "I'm being kind letting you control your head".
Jeff couldn't believe that he was terrorised of his younger 15 years old sister reduced as his pussy, she already had a twisted and manipulative mind. "Let's go to the important" she talked again, grabbing a dildo and a egg shaped vibrador, controlling Jeff's body to spread his legs on the bed.
Jeff just felt and watched in horror as everything happened against his will, just having to let his sister have fun with his own body, inserting the 7 inches dildo in the depths of his pussy, or Melanie's mouth. For Jeff it felt like he previously sensed, just masturbating his new sex organ, but for his sister she felt the same feeling as Jeff as her womb and vaginal track were both parts of them, but also like giving a blowjob, using her mouth to swallow and spitting it out, she was drowning in a weird but great pleasure, and Jeff too even that he didn't wanted to admit it. Minutes later she kept playing with themselves until they came again, Jeff moaned while Melanie took off the dildo and vomited the cum again.
"Yayyy your second orgasm, just wait, there will be even more later!!" Melanie exclaimed while Jeff tried to recover from the tiring session. "While you rest I'll do a little thing more~" she again controlled one of Jeff's hand to grab the vibrator, turn it on and swallow it with her pussy mouth, keeping it inside, stimulating both of them.
"Y-you, idiot" Jeff blushed feeling the vibrations in his insides. "And it will feel even more exciting while we walk!" Melanie could still talk, as the vibrator felt like having it in the middle of her long throat, actually Jeff's vaginal track, but without wanting to vomit it or swallow it, she could willingly control that and expell it when she wanted.
As Melanie said, Jeff stood up against his will, feeling the vibrations even more intense as he walked, not a single action was taken by him but his vaginal sister. "Let's see what else we can do big bro~" she said looking around, thinking on using the powerful computer again, seeing someone in their new shared form or something else, Jeff knew that no matter what decision his sister took he wouldn't enjoy it.