If I must.

"Please, John? I know you just came, but I need more. I'm sorry I let it sit out, but this time you can cum right in my mouth. I promise I won't waste it. Please? Can I have more of your cum?" says Sara, as her hand slowly strokes up and down your shaft.

Holy shit. She's practically begging. you think. Even though you'd just came, you knew it wouldn't be too difficult for you to go again. A speedy recovery time and large volume of semen produced were two of those "exacting criteria" that all donors in the program were vetted for, as well as the requirement that their semen contains a higher-than-average concentration of the particular proteins that the afflicted "cum addicts" require for their treatment. You, luckily, are among the top percentiles of everyone who has applied for the donor program. When giving you the results of your test, your lab assistant Jenny told you you had "the perfect cumshot."

"Yeah, Sara. Of course," you say. "I told you I'd do anything I could to help and I meant it."

She grins, flashing her perfect smile.

"Okay, so what do I do this time? Just kneeling here and letting you do everything didn't work."

Her makeup is something of a mess, after crying earlier and then you covering her face with your huge load, but she's still a beautiful young girl. Could you get her to...?

"Ah, uh... Hmm... Have you ever given a blowjob before, Sara?" you ask, somewhat tentatively, doing your best to sound like a doctor asking a clinical question and not like a man desperately wanting a young girl to wrap her throat around his cock.

She grins again, shyly dipping her gaze from yours.

"Yeah. I mean, I had a boyfriend in High School, and I blew him a few times. But he was... His, uh, penis, was... You have a really fucking big cock, John. It's huge. Like, I don't even know if I could fit it in my mouth." Sara keeps stroking your shaft as she says all this, but you notice her left hand has found its way under her miniskirt. Her eyes are now totally focused on your cock. "Can Nicole do it?"

Oh, right. Nicole... She said she was cool with this, but I still don't want her to walk in on me with my cock in her sister's mouth. She said she was going to the gym. How long has it been since she left? You'd honestly believe it if someone told you it had been five minutes or two hours. Every second since you'd gotten home had been so surreal and incredible that time ceased to exist. Better hurry this up.

"Yeah, Nicole can do it. It might be tough fitting it all the way down your throat at first, but don't worry, it'll get easier the more we do it. In the meantime, just kiss it and lick it all over. It's just like sucking on a big popsicle... with less biting... No biting. With no biting."

After you tell her that her sister can swallow your cock without trouble (only a minor exaggeration), Sara dives in.

She starts by planting a long wet kiss on the head of your penis, rolling her tongue over it. Then she moves to licking up and down the shaft over and over, sloppily slobbering on it. Then she takes a deep breath, and starts to fuck her own face. She goes deep, surprising herself, and she holds herself there for a moment. You can feel her tight young throat convulse around the head of your cock as she gags. She slides back off to catch her breath. "Hey, I can do it!" she says proudly, and then she stuffs your dick back down her throat.

Fuckin' A. Sibling rivalry at its very best.

"Lick my balls, baby," you say, caught up in the moment.

Without hesitation, the teen girl pops your cock our of her mouth, latches her lips onto your scrotum and laps her tongue across your nuts. After a while, she switches back to aggressively deepthroating you.

You're lost. In time and space. Your mind is overloaded with how perfect this moment is. You've got a gorgeous teenage girl in front of you with her nose pressed against your pubic bone and your balls on her chin. Her tongue and throat are both working overtime, trying to coax another load of cum out of you. She's no longer trying to hide that she's masturbating, you can smell her pussy as she works her fingers up under her skirt and moans into your cock. Then, something even more incredible happens.

Sara pulls your cock out of her throat, sits up on her heels, and slaps your dick between her huge teen tits.

"Oh fuck," you groan, as she presses her massive mammaries together around your cock. She works her jugs up and down your dick rapidly, well-lubricated by all the throat-slime she slobbered out over the past few minutes.

"Come on, John," Sara breathes out as she works her mammoth assets up and down. "I need your cum. Give it to me, please. Give me your fucking cum. Please. Please. I fucking need it. I fucking need your cum, please give me your fucking cum."

You feel a familiar feeling at the base of your ballsac. "Fuck, I'm cumming!" you manage to blurt out just in time.

This time, Sara doesn't hesitate. She dives back down and wraps her lips securely around the head of your cock and as you fire off rope after rope of thick jism onto her hot tongue. Sara's mouth overflows and some of your load runs down her chin--she manages to catch it in an open hand. She swallows hard, clearing a mouthful of your cum as you continue to pump more into her. When you finish, she pulls back off your dick, swallows again, and then slurps the overflow off her hand and chin. You both sit silently for a moment, you, pantsless, in the chair, Sara kneeling topless at your feet. Then you both notice a single drop of cum appear at the tip of your dick.

You both notice each other notice. Sara grins, and you chuckle. As you're laughing, Sara reaches over and slowly licks the head of your cock, capturing the last drop of your sperm on her tongue.

"Thanks, John," she says looking up at you from her knees. "I really needed that."

"Hey, any time. Really. It was, uh, it was my pleasure, Sara."

The two of you clean yourselves up. Sara goes in to take shower while you sit on the couch and pretend to watch television, but really you're just replaying the events of the afternoon over and over in your head. After a little while, Sara comes out of the bathroom dressed back in her knockout outfit with her makeup reapplied. Before you can talk yourself into trying to fuck her mouth again, you go take a shower. A cold shower. After washing and getting dressed in your favorite pair of jeans and a plain black tee, you head back into the living room. When you come out, Sara has apparently gotten to work in the kitchen preparing dinner. You can tell from the black acrid smoke starting to fill the apartment.

"Jesus! What's going on in here Sara?" you ask, quickly turning off the heat on the stove and opening the kitchen window as wide as you can.

"Fuck, I'm sorry, John!" she says "I just--I got distracted. I was trying to make dinner for us, as a thank you for you and Nikki letting me stay here and you agreeing to be my donor and everything, but then I started texting with my friend Alicia, and I lost track of time."

"Shit, yeah, I'll say," you respond. "Ugh... What was this supposed to be?" She doesn't answer. Whatever it was, it was pretty solidly burnt. You throw it in the sink and run cold water.

"God damn! What happened in here?!" shouts Nicole as she comes into the apartment.

"Your sister decided to cook for us, and almost ended up cooking us," you reply.

"Sorry, Nikki. It was to say thanks for letting me stay here and for John agreeing to help me with my, y'know... my problem."

Nicole pokes the mess in the sink with a serving spoon, and turns it over.

"Well, I guess it's a good thing it burned, or else we'd have had to eat it," says Nicole.

"Oh, c'mon! My cooking isn't that bad!" Sara laughs.

"Well, if it tastes as good as it smells, I'm going to have to side with your sister on this one," you say. "So, since the apartment smells like ****, why don't we go out for dinner? You girls feel like Chinese?"

"That's a great idea," says Nicole. "Let's go to Hunan Palace, that way we can stop at Sara's place and she can pick up some things."