A fat bulge grows on Zoe's crotch

Her female jeans is not designed to house such a thing. It stretches the fabric making your sister visually umconfortable. She unbuttons her pants and looks inside her panties.

"Hahahahahahahah." She laughs like a bloodthirsty maniac. Chills are sent down your spine by how crazy she's acting. Zoe makes herself comfortable on the couch. "Oh man, I've always wondered what it was like to have one of these."

Your sister pulls down her pants and underwear to reveal a massive cock, balls, pubes and everything. It grosses you out to see such a thing between a girl's legs. Zoe also looks far too relaxed with it, which adds to your general unease.

"What are you waiting for?" You hear her speak.

"What?" You reply in confusion.

"Well, you said you would do anything and I want to know how it feels like..."

"No!" You exclaim as you just now start to understand what she was asking of you. "I'm a guy Zoe, don't ask me to do this..."

"You'll never be one again if you continue with this attitude." She says nonchalantly. It feels like an eternity passes before you make a decision, one that will change your life forever.