"Sorry, sis, I got really important things to do, maybe an other time OK?"
"But you always says that! You just don't want to play with me!"
"No, I do want to play with you! But here this is really important for me! I promise I will play with you next time, OK?"
"You always promise, and you never did it! You just don't hunderstand how I feel! Sometimes I wish you were a girl, because if you were, You would play with me!"
"Granted!"
You don't know who said that, but you know that there is someone helse in this room. Then you see the lamp shining, and some light hits your chest. You feel your hair growing more and more, until they're ones of girl.
"What the..."
You then feel like you were becoming more petite, more delicate. You feel your muscles and your body hair shrink. But those are not the only things that shrink. You feel like some pleasure around your crotch. Panicked, you grab your cock, but nothing can stop the transormation. As you feel your newly vagina, you feel like a pressure on your chest, and you notice that you now have C cup boobs! Your body have finishing changing, and as you're so shocked to do anything, you now feel make up applied on your now delicate face, and your clothes are becoming way more feminine
"Hello master, what is your next wish?"
When she sees that, your sister seems to be as shocked as you.