The one who opens the door is a teenaged girl, wearing a pink tank top and skin-tight white pants. You immediatly notice thar her boobs are quite big for a teenaged girl, at least a C-cup. Her face is familiar, as she reminds you of your younger brother Ben... But the bulge on her pants reminds you she must also have a big dick.
"I am sure Celia wants to break up with me" she says, without being bothered or commenting on your nakedness. Your sister continues: "Yesterday evening, Celia's mothers were both out of town, so I went to my hermfriend's house. It was nice, but she wanted to fuck my pussy, but I am not ready to give her my pussy-virginity. Or my ass. Celia's dick is so big, even bigger than Mommy's or yours; I am sure it would tear me in half !" Your sister (what is her name in this reality ?) says all that while removing all her clothes. She is now as naked as you are, and you can see she is a hermaphrodite like you, a beautiful 15-years-old girl with a 10-inch long penis above her pussy.
Your brain slowly adapts to the reality of this world, as you understand that your sister has a hermfriend named Celia; that your sister knows about your Mother's dick (and yours, but not surprising as you are currently naked); that sexual intercourses are way different in this reality, and that your sister has no shame nor hesitation to discuss about them with you, and that nudity seems so casual in this world - at least among siblings.
You ask your sister: "So, what did you do?"
"I didn't have the boobs to say "no" to her, so I offered Celia a blowjob and swallowed all her cum. But it wasn't enough for her, she really wanted to fuck my pussy. She often says it's unfair, because she let me fuck her pussy and her ass, and I don't let her do the same with me. But I'm only 15 ! I am not ready. Girls in my school want to date me simply because I'm the sister of the famous porn star, Pussykate Waters, and they assume I am a bottom like you. They don't get that I prefer to be a top, no matter what I tell them."
The poor girl needs help from her big sister, but how can you help her if you know nothing of this reality ?