The Duncan Family had a weird genetic thing. Every male in the family got a large cock. Guaranteed. With one twist. Not for the males of course. No. For the females. There was a 90% chance that the female members of the family would grow a member upon reaching puberty. Member. Meaning penis. They grew a cock. It replaced the vagina. Pretty much overnight. Doctors weren't exactly sure what caused it. Tests are done every once and awhile. But nothing comes of them.
The other thing this did was make puberty an extremely horny time for everyone. So the Duncan siblings fucked. P.J. fucked Teddy's ass because he had the biggest cock. Teddy fucked Gabe up the ass because Gabe's cock was smaller than hers. For now. Gabe's cock was growing. Soon he would be bigger than Teddy. And he would have Teddy's ass too. Maybe Teddy would even have two cocks up her ass. These were difficult times for Teddy. And it was a very big possibility that Charlie would go through these changes as well. So Teddy recorded video diaries for her about what it's like having a cock.
Teddy and Gabe were currently jerking their cocks together. Up against each other. With lots of lube.
"My cock is still bigger." Teddy says.
"No, they're the same size." Gabe says.
"They're the same size when I can't hold you and butt fuck you anymore." Teddy says. She turns Gabe around. She rubs her lubed cock on her brother's ass. And then pushes in
Gabe sighs. Only a few weeks longer and his cock should be bigger. He'll show Teddy a real ass fucking. But now he's got to take Teddy's cock in his ass. She goes in and out. Fucking his ass. Slowly. Building up speed. It's not that he doesn't like getting ass fucked. It's just embarrassing. He's glad that Jo has never seen him like this. It's embarrassing to be fucked in the ass by your sister. It's embarrassing for your sister to make you cum from anal sex. He'd rather be cumming in her anus. And making her cum.
Just then PJ comes into the room.
"Teddy! There you are." He says. He's naked. He's erect
"What do you want?" Teddy asks. Still fucking Gabe's anus.
"I'm horny. I want to fuck you. What do you think I want?" PJ says.
"I'm a little busy. Can't you see?" Teddy says.
"Ah but I am the oldest. And the biggest. So I get first dibs on pleasure." PJ says.
"Can you let me finish just this once?" Teddy says.
"Nope." PJ says. PJ grabs Teddy and leads her away.
"You better not move from that position." Teddy says to Gabe.
PJ leans Teddy over and take his own lubed up cock and rubs it on her anus. He pushes in. He fucks Teddy. Teddy moans from pleasure. Her cock is still erect. Her balls ache for release. She'd rather have release from fucking Gabe's anus. But she's not going to be able to do that much longer. And she knows that. She's going to try and fuck Gabe's anus as much as she can over the next few weeks. But PJ is obviously going to be a problem.
PJ fucks Teddy's anus harder. The pleasure builds. It builds. Teddy cums. Ropes shoot out from her cock. Fertile loads of cum. Fertile loads she'd rather be shooting up an anus. Fertile loads that her changed biology would rather be shooting up in a girl.
PJ shoots his ropes of cum up Teddy's anus too. Filling her up. He leaves her with cum dripping. Satisfied. Teddy gets up and goes back to her room. Gabe hasn't moved.
"Good boy." She says.
"Fuck off" Gabe says. Teddy shoves her cock up Gabe's anus as fast as she can to shut him up. She pounds his anus. A lot. Very hard. It takes her a long time to cum. Because PJ just made her cum. She makes Gabe cum twice before she herself cums in his anus. She pulls out.
"I'll get you back for all this." Gabe says.
Teddy slaps PJ's cum from her anus on Gabe's face. "Love you too." She says.
Yes, it was a regular day in the Duncan household.