Your tits grow rapidly to double, if not triple, EEs and your hips flare out as your ass grows to a size any girl would envy. You attempt to question her motives but all that comes out is a soft moan as your body becomes that of a sex maniac.
Your lips become big and puffy, perfect for sucking cock or pleasuring your new Master. You look in the mirror to see the make up on your face and your new feminine features.
Your fingernails get longer and turn a deep red, and tiny rings appear on them. You press a button on one curiously and it begins to vibrate. Your sister grins at you and tells you to try it. As if you couldn't control your hand, you do it...and like it. Your other hand squeezes your breasts as your finger works your pussy and has the other fingers stroke your clit.
You continue for several minutes until you hear your sister clear her throat. You look up and see she is now naked, her glorious tits on display, and wearing a large strap-on dildo. "Let's have some fun..." she says, grinning wickedly.