Your sister is the biggest slut. You've heard it all around school, about the photos she sends guys. She says its just for her boyfriend, but you know better. One night, you hear her giggling, her phone camera shutter clicking, so you decide to sneak into her bedroom. You find her, all dressed up in this slutty outfit, taking pictures. You watch her, completely oblivious to your presence, as she pushes her tits out, arches her back, pulls her cute bra down a little...and your mind starts to scheme. See, if your parents knew what she did with that phone, they'd take it away immediately. She'd be sans-smartphone til graduation! That's leverage. That's blackmail fodder. So you clear your throat, watch her jump. And you propose a little agreement.
"You want to look at the photos? Are you serious?! You're my brother!" But after a few more threats, she's flipping through the pictures for you, showing you each one. And next? Well, next she's going to continue her little photoshoot just for you. Her eyes widen. Yup, that's right, you tell her, start snapping. You want to see where it was going. She pleads but its no use. Get naked for her brother, or become a social pariah. You watch as she starts to pull down her shorts, take her bra off. Your cock has stiffened. You're sure she's noticed, pausing before she starts to play with herself, not sure if she wants to encourage your raging hardon. But does she have a choice? Of course not.
She slides forward, naked, splayed before you. "You know, maybe...maybe you should take that out. You know, if you want to..."