Yes, but she can only touch.

You can't stop yourself this is your sister but after just your mom's equally absurd breasts grazed you this morning you can't resist that offer. So you sit on the edge of your bed as your sister strips off the tiny t-shirt she is wearing. With a bit of effort and a grunt from her the struggling fabric is removed, and out drop the biggest perkiest breasts you could imagine, like they made the most stacked pornstar look flat in comparison. Yet it was clear from the bounce and the perfect blemish-less skin these were all natural.

You sit on the edge of your bed and remind her that she can only touch, to which she gives a mocking little salute with a "scouts honor." Then before you can say another word she plops her phat pillowy ass on your lap and in response your cock goes between her legs and gives her stomach a light slap. Your now full mast cock coming just below her cleavage. She then takes your cock in her hands and begins lightly stroking it, "Goddamn bro if I knew you had this I wouldn't need boyfriends."

Your hands reach up and take the impossibly giant titties into your hands, feeling their weight and watching as your hands were lost in them. Then you can feel from your waist the soft thong your sister wears that is the only thing separating you and your sister as siblings right now. You then respond to her statement "What do you mean by that?" Yet before you can get an answer you realize that you have a audience.