Your younger (futanari) sister

You hesitated as the name popped up in your head. Your first reaction was almost like a revelation, the moment a vision sprung in your head. Carrie noticed your hesitation.

"What's wrong?" She asked, coiling her arms around you, tickling your ear with her warm breath. "Got cold feet already? I was almost looking forward to it at this point." After another moment's hesitation, the name finally slips from your lips.

"Samantha."

"Your sister?" Your girlfriend furrowed your brows. "I suppose it'll be the first time I get to play around with a woman. And her abs are quite nice. But I thought you said you wanted me to be used by men."

"No, it's not that," you shook your head. "Actually, Sam has a secret of her own. You see, she was born with a rare condition called futanarinism."

"Futanarinism?" Carrie tilted her head.

"Yeah. It was first medically recorded in Japan in the late 19th century. It's a genetic abnormality where clusters of XY chromosomes develop around a female baby's genital area before birth..."

"Oh, I've heard about that! They have dicks instead of vaginas, don't they?" Carrie's face flashed with realization. "Wait, your sister has a penis?"

Your face blushed. "Yeah, she does. Part of the reason she hits the gym, — she needs to burn off that pent-up energy and testosterone. She's kind of self-conscious about revealing it to others, though, so I was technically not supposed to tell you..."

She nodded her head in understanding. You continued, "Anyway, she finally managed to get a full-ride scholarship for our nearby alma mater and she's been pestering me about it ever since. Apparently, mom doesn't want to do anything with financing her housing."

"Really? Bell University is a very prestigious, private college. You remember how we had to work our ass off just to get in on a partial scholarship!"

"Well..." You scratched your head. "She only got her scholarship here due to her condition. And she dropped out of another college with failing grades, so she and mom aren't exactly on good terms, let's just put it like that."

"I see..." Carrie mused. "So what's she like?"