Kitty humped up against Paul's thrust as she felt the head of his cock swell and begin to spit its dangerous load at her cervix. The warmth and slickness of his jizz and the way his eyes rolled back as he lost control and emptied his prostate into her triggered her own climax, and she writhed against him while the walls of her cunt squeezed and milked his spewing prick for every last drop of sperm.

Finally, he collapsed on her, while her vagina continued to massage his prick for anything left inside.

'That was so good, sis, ' he gasped when he could speak again.

'Yeah, well, it'll be the last time for a couple of weeks, ' she said. 'Can't be doing it again or I might get pregnant.' She felt his cock, which had been slowly wilting inside her begin to stiffen and grinned. 'You may think it's a good idea to get your sister pregnant, but there are some who wouldn't agree — your sister for one. Fucking is one thing, getting a kid is another.'

He slid his prick back and forth in her cunt, stirring the sperm it was keeping bottled up. She tensed her muscles so that the sleeve of her vagina gently massaged his reviving member. He dipped his head and ran the tip of his tongue round her nipples, flicking them until they stiffened, the sensations they produced causing her to screw her hips against him.

His cock was now as stiff as it had been ten minutes earlier, and he began to drive it into her. He kissed her.

'One more fuck now while you're still full of sperm anyway isn't going to be any more dangerous, ' he said.

She smiled lovingly at him. 'I wouldn't do this for anybody else.'

He began powering his prick in and out of her. In fact, she loved her brother, and enjoyed fucking him as much as he enjoyed fucking her. That their relationship was strictly frowned-upon by all and sundry, and discovery by their parents would be disastrous, only seemed to make their coupling more exciting.

Kitty had been fucked by a couple of boys at school: her virginity had been taken, somewhat heedlessly, by the captain of the school football team, celebrating after scoring the winning goal in a match against their nearest rivals. He'd seen her, jumping on the sideline with excitement, and taken her behind the changing rooms where he'd simply leaned her against the wall, pulled her knickers down and the short skirt she was wearing out of the way before sticking his fat 8-inch cock into her previously-unused and very tight vagina.

There had been so much pain at first, caused by his size, that she never noticed the loss of her hymen. She was beginning to think that fucking was not all it was cracked up to be when the rhythm of his thrusts began to have a pleasurable effect on her.

Standing up had never since been her favourite way to fuck, but on that occasion, it made him slow to reach his climax, and by the time he did she was ready. Her knees were on the point of buckling when he powered his cock into her with a grunt, his face red with the effort, and for the first time she felt a man's spunk fill her cunt. It was a massive load, and it blasted against her uterus with enough force to trigger her own orgasm.

She took a week a recover and was thinking of encouraging a repeat performance when her period came on. She told him regretfully he'd have to wait. He said he didn't care, she was such a good fuck, and anyway fucking during a period was one of the those times she couldn't get pregnant.

They waited a couple of days while the worst part was got over, then in a more comfortable position on the bed in the school's first-aid room, they'd fucked like rabbits as often as they could for a fortnight.

Word got round. A month later, the football captain brought a mate along. The novelty of being fucked by two young men in succession she found interesting, adding to the excitement, but when, as her cunt was sucking the captain's jizz into her bleeding uterus, she saw her brother Paul in the doorway, a frown on his face, she'd realised she could be in deep trouble, especially if he told their parents.

He watched for a moment, his expression inscrutable, until the captain finished and rolled off her, leaving a messy mixture of sperm and blood between her legs which Paul couldn't help but see.

The captain seemed unconcerned.

'Kitty's hot to fuck, if you're interested, ' he said. It seemed then that recognition dawned. 'Oh, you're her brother. Tough. But you should be proud of her, Paul.'

Paul had smiled strangely and looked at Kitty.

'See you at home, sis.'

'Yeah. Sure, ' she replied, chastened, as he left them.

Kitty and the captain cleaned themselves up with towels and she fixed a clean sanitary towel in place in her panties. Her skirt had simply been pulled out of the way and her blouse shoved up round her neck, so they didn't require much attention to put her clothing back in order.

'See you tomorrow, Kitty, ' said the captain.

'Uh, yes. Mebbe.'

When she got home, she grabbed a glass of milk from the fridge before making her way up to her room. She needed to change her clothes, and wondered what her mother would think if she smelt all the dried spunk on her knickers. The sanitary pads tended to mop up the sperm leaking out of her along with the blood, and so far, her mother had apparently not noticed. The other problem she had was the worry that Paul might tell their parents. They would undoubtedly go ballistic.

She went towards her room, which was beyond Paul's, at the end of the landing. As she passed his door, she heard him grunting. Curious, she opened the door quietly, and saw him on his bed, his trousers and underpants on the floor and his shirt open, stroking his cock with his left hand.

He turned his head and saw her, letting go of himself. She noticed that her brother was as well-equipped as the football captain. She came and stood by him.

'Don't stop on my account, ' she said. 'Perhaps I can help?'

She wrapped her hand around his cock and slowly wanked it. Paul drew in his breath and gritted his teeth.

'I'm gonna come, sis, if you don't let go.'

She had an idea. She let go of him and reached under her skirt, pulling down her knickers and stepping out of them, while he watched her with awed fascination. She climbed onto the bed and positioned herself astride him. She had the idea that if she fucked him, he would keep his mouth shut and not tell on her.

Taking his cock, she slid it backwards and forwards on her cunt lips, so the pre-cum that was oozing from it lubricated her and encouraged her own juices to flow. When she was slippery enough, she simply squatted down so his cock slid inside her.

'If you're going to come, best not make a mess of the bed, bro, ' she said, sliding up and down his prick and feeling it lurch inside her. Paul began thrusting his hips up each time she descended on him until their pubic bones ground together.

'This. Is. All. Wrong. You. Might. Get. Pregnant, ' he gasped in time with his strokes.

'You can try, brother, but I don't think you'll succeed. Give me your best shot, Paul!'

She ground her cunt down as far as she could, feeling the waves of orgasm spread out from her cunt and envelop her whole body. Her cunt squeezed and rippled against his cock without conscious effort on her part, triggering his orgasm. His balls swelled for a moment, then the sperm travelled up into his prostate which fired dollop after dollop along the tube in the base of his cock, until it was belched, spat and sprayed out of the tip against the entrance to her womb.

The sensations of his cock throbbing and beating inside her triggered another orgasm in Kitty, from which she collapsed forward onto her brother's chest.

It was the first of many fucks she and her brother had.

They'd discovered that in addition to the week of her period, it was fairly safe for up to ten days after. Some people said two weeks, but sperm could live in a vagina for three or four days, so they decided on a ten-day limit. Fucking after her period was a lot pleasanter than during it, though sometimes they couldn't wait.

Kitty gave up fucking the captain before he invited the whole team to fuck her, unwilling to become the school slut. It was more convenient and comfortable fucking her brother any time their folks were out. Happily, both parents had jobs which involved them in long hours and evening entertaining.

Within a few weeks, it became harder and harder to stop fucking at the ten-day cut-off point. Neither of them dared bring any contraceptives into the house, as their parents, staunch Catholics, would have been furious. They'd told their children to remain celibate until they were married and expected that edict to be obeyed.

Which was when Kitty had the idea of bringing another girl from school, Millie, into the arrangement.

'You're not serious, are you?' asked Paul. 'She's ugly.'

'She's got nice legs and her boobs are okay.'

'I know, but ... I know there's nothing actually wrong with her face, but her eyes are ... and her nose is ... I just don't find her very pretty.'

'But she's perfect in every other way, Paul, ' said Kitty. 'She doesn't have a problem with contraception — she told me if she ever got in a relationship she'd be straight on the Pill or something. She likes you, and there are no other boys after her, probably for the same reasons you have, so she's clean. And because she's never had a boyfriend, she's climbing the walls with frustration. Show her a bit of interest and she'll throw herself at you.'

He pursed his lips. 'You've spoken to her about this, haven't you?' he asked perceptively

'Well, I asked how she'd feel if someone I knew fancied her and wanted to fuck her. She seemed very keen.'

'So the arrangement is that I fuck you whenever you're available and Millie stands in when you're not.'

'Or lays in, more accurately. Yes.'

'You're mad, ' he said without heat.

'No, I'm just very practical. What do you think it's going to be like for me when you're fucking her?'

He hadn't thought of that. 'What about Sarah?'

Their sister was just thirteen.

'What about her?' asked Kitty.

'Well, could we get her to get you off when it'd be dangerous for a man to do it?'

'You might, ' said a voice from the doorway. Sarah stood there in her school uniform, minus shoes which she'd taken off downstairs when she came in.

'Sarah!' exclaimed Paul. 'Didn't know you were there.'

'There's a lot you don't know, brother, ' said the girl. 'I know, for instance, that you and Kitty have been fucking each other for ages.'

'Well thanks for not telling mum or dad, ' said Kitty.

Sarah came into the room. 'And I'll go on keeping your secret, but only if I can be a part of it.'

'What do you mean?' asked Paul.

'I want you to fuck me too. You can do it when I've got my period and just after, like when you fuck Kitty.' She smiled suddenly. 'See: not so difficult. And with two of us to fuck, you might not need Millie at all.'

Paul stared at her.

'You've forgotten one thing, Sarah, ' said Kitty.

'What?'

'You and I — and mum — are pretty well synchronised. It's what happens when women live close together under the same roof. So when I can't fuck Paul, you can't for the same reason.'

'Oh.'

'But while he fucks Millie, we can do each other, and I'm sure that when we're both available, he can spare some sperm for you — eh, Paul?'

'Uh, yes. But she's only a kid.'

Sarah frowned and approached the bed, grabbing his prick. 'Say that again and I might not co-operate, ' she said. '"Old enough to bleed is old enough to breed" I read somewhere.'

'You have some funny reading material, sis, ' he said.

Kitty broke into their discussion, which threatened to become an argument. 'Right then. I'd better see Millie and get her on the team. She might need time to get her contraception sorted out — but next month, wa-hay!'

She giggled, and she and Paul got dressed before their parents came home.

Three weeks later, Paul, Kitty, Sarah and Millie were in Millie's bedroom. Her parents had gone out for the weekend, and they were all stripped to their underwear, sitting on her bed.

Millie was looking warm and not particularly attractive, though, as Kitty had said, she had well-formed legs and a cracking body. It was just a shame about her face. At the moment, she was bright red, whether with embarrassment or lust, Paul could not tell. He didn't care much.

'So tonight's your tenth night, is it Kitty?' asked Millie for the umpteenth time.

'Yes. It's the last night Paul can fuck me safely.'

'Or me, ' said Sarah, her lower lip trembling.

'You realise you're too young, ' said Millie to the younger sister.

'You realise you're just Paul's cum-dump?' replied Sarah, saccharin-sweet.

Millie ignored her and looked at Kitty and Paul. 'And you're going to fuck now, while I — we — watch, then tomorrow night, I sort of take over?'

'If Paul's got any sperm left after I've finished with him, and can get it up again, you can have him tonight, if you want, ' said Kitty, generously.

'And what about me?' complained Sarah.

'You're too young!' This time, Kitty told her. 'Be grateful for what you're gonna get out of it. We can try that later, if you like, ' she added, 'though I don't know what it'll be like, trying to fuck a tight little girl.'

Millie turned even redder for a moment and reached under the bed. 'This might help, ' she said, holding up a large vibrator in the shape of a fairly big prick.

Sarah stared. 'You think that'll fit in me?'

Kitty smirked. 'It'll fit in me.' She had, after all, entertained the football captain in her cunt, and the dildo wasn't as big as him.

'Hm. I'm sure I can do anything you can, ' said Sarah.

'I've got some K-Y, ' said Millie, 'that helps.'

'Right then, ' said Kitty, sliding her hand down Paul's underpants, 'time we got going.'

Paul's cock for once did not respond easily to her touch.

'I suppose it's because there are three of us, ' said Kitty. 'Come on, girls, let's get our clothes off, maybe that'll help.'

She pulled off her blouse and skirt as she spoke, while Millie and Sarah slipped out of theirs more slowly. Kitty unfastened her bra and rubbed her nipples until they stood out stiffly, then slowly wriggled her knickers down her long legs, finally sitting on the bed in front of Paul, her legs splayed, and allowing the fingers of one hand gently to rub at her slit. Millie, meanwhile, was gently rubbing his prick, which at last showed signs of interest. Paul leaned forward and let his fingers explore Kitty's breasts, dipping his head until he could take a nipple between his teeth and gently suck on it. Kitty sighed with contentment.

He slid the fingers of his free hand through the light down on her mons, and between the lips of her cunt, until he could feel her heat and growing moistness. At the same time, he lifted his lips to hers and kissed her, letting his tongue explore her mouth. Kitty grabbed him round the neck and pulled him with her as she laid on the bed, her legs bent either side of him like a cradle.

He felt another hand take his prick and wipe the pre-cum oozing from the end along Kitty's buttery slit, before lodging the tip in her hole and gently massaging it to encourage him to press home.