Your sister Crystal walks in.

"Well, well, well. What's going on here?" your sister Crystal asks as she walks into the room. As if that wasn't obvious with you kneeling in front of Sarah's cock, cum dripping down your chin.

"Hey, sis! Doug just gave me a blowjob, and it was amazing!” Sarah replies excitedly.

"Is that so?" Crystal asks with a smirk.

"Yeah! He even took my whole dick in his mouth! You should get him to give you one too."

"That sounds like a good idea."

You are too shocked by the way your sisters are talking about you to respond and just kneel there as Crystal approaches, pulling off her jeans and panties.

"Is that true? Did you deep throat our sister?" she asks as she stands in front of you, stroking her slowly hardening cock.

"Um...I guess...but…" You try to explain that it wasn't really your choice to take her all the way, but you have a hard time getting your words out, distracted by the monster growing in front of you.

"I think you'll find my cock a little harder to swallow." You can't deny her words. It's already as large as Sarah's, and isn't even finished growing yet. You quickly shut your mouth and look up at your sister in apprehension.

"Well, go ahead and get started" she tells you. You keep your mouth closed and shake your head. Giving Sarah a blowjob was embarrassing enough, but giving one to Crystal too?

"What? You'll suck Sarah's dick, but you won't suck mine?" You keep your mouth closed.

"Do you love her more than me?" she asks with a pout.

"No, of course not, but..."

"Great!" Crystal says and pushes her cock into your mouth before you can finish your reply.

You try to back away, but your sister grabs your head and holds it in place. She forces your head back and forth, fucking your mouth with her cock. It fills your mouth completely, your jaws straining around it, gagging a little every time it reaches the entrance to your throat. You're only getting about a third of your sister's dick, but she seems content with fucking your mouth, leaving your throat alone for now.

You glance over at Sarah and see her stroking her fully erect dick, eyes filled with lust as she watches you suck Crystal off.

"Yes, Dougie, suck my cock!" You realize that Crystal is no longer holding your head and that you are bobbing up and down her dick on your own. You have to admit that it feels wonderful having your mouth filled with girl-dick; your own dick is straining against your pants in arousal.

"Okay, Doug. Time to see how deep you can take me."

You take Crystal's cock into your mouth as far as you can and push forward, trying to get it into your throat, but it's just too big.

"Relax your throat, Doug, and keep swallowing. It will go in."

You grab your sister's hips for leverage and slowly try to pull yourself forward. Crystal's dick isn't that much thicker that Sarah's, so you know you should be able to get it in. You follow her instructions and keep pushing forward. Your diligence is rewarded as you feel the head finally enter your throat.

Crystal moans in pleasure. "Yes, Doug. I knew you could do it."

You pull back so you can take a breath and then push forward again. It's a little easier this time and you're able to go a little further. After a few more tries, you are excited to see that you've taken over half of your sister's dick.

"Oh, yes. Keep going." your sister urges you on.

Each time you press forward, you're able to go a little further. Finally, with a moan of triumph, your nose touches your sister's stomach, and her entire dick is in your throat. You hold still for a moment, enjoying the feeling of your throat stretched around this glorious girl-cock.

"Wow, Doug! That's amazing for a newbie. Most of my boyfriends haven't been able to swallow the whole thing."

Eventually you need to breathe and pull yourself off. Once you have caught your breath, you push forward again slowly, reveling in the feeling of Crystal's cock working its way down your throat again, so warm and smooth. You start moving faster now, back and forth, taking it all the way down and then back out. Your sister's soft moans let you know how much pleasure you're giving her. You can't believe you are enjoying this so much.