Sexy Fun Times/Wank/Hang/Shower/Leading/Swallow
She looks up at you and smiles. "I want it," she says.
Seconds later, your knob-head is back in her mouth; she takes a deep breath in through her nose and presses down, but her gag reflex makes her pullback. She tries a second time, and this time she has to lift right off and you get a tissue just in time to catch a mouthful of saliva. She wipes her lips with the back of her hand and dives down again. " If that's what she wants, " you think and this time you put your hand on the back of her head.
She tenses up for a second and then, realising what you got in mind, you feel her relax. You've only ever been deep-throated once before, and that was with an experienced woman; even though there's still quite a lot of cock outside, the feeling of the head going into her throat and the knowledge that it's your ten-year-old sister's, makes you come instantly.
As soon as your cock comes out of her mouth she brings most of the spunk straight back up all over your lap. She's coughing and spitting, but that triumphant look is back again. You pick her up and carry her into the bathroom; moments later you're both under the shower and when she starts laughing she sets you off until you both collapse on the floor of the shower in fits of laughter and giggles.