It was a lovely afternoon. I was swimming in our houses pool while Asuna was sitting on the tiles around, with her legs in the water and swinging them lazily. She was wearing her white bikini.

I swam over to her. 'Don't you want to dive too?' I casually asked, leaning on her knees.

'Nah. I'd rather sit here and enjoy the breeze,' she answered, closing her eyes and taking a deep breath.

'You're so uncool sometimes,' I pouted.

She dropped her upper body and, now lying in a lateral position, momentarily opened her eyes and stuck out her tongue.

That moment, Suguha returned home, carrying bags full of new things. Obviously, she had been to the mall!

'Hey, guys,' she said while passing by. 'I'm going to my room to prepare for my sleepover with my classmate, Tia, tonight.'

'Okay, have fun,' I called out.

Suddenly, the younger girl stopped and turned around, with an enigmatic smile. 'Do you guys want to come?' she proposed.

'I don't think this would be right,' Asuna answered with a smile. 'This is supposed to be time between you and your friend. You don't have to take us everywhere you go.'

'That's right,' I added, still leaning against Asuna's legs. 'Just because we have threesomes doesn't mean we can't have separate lives as well.'

Suguha beckoned to Asuna to approach. The curious redhead took her legs out of the water and walked over to the brunette. Suguha whispered something in her ear. Then they both giggled.

I raised an eyebrow. 'This will be fun,' I heard Asuna whisper.

The girls turned to me. 'You know, Kirito,' my official girlfriend said with the same enigmatic smile as Suguha. 'On second thought, I think we should accept Suguha's invitation.'

'Umm... okay. If you say so,' I scratched my head. What were they up to? Was this going to... a foursome? Was that Tia chick naughty like my sister? Was she beautiful? Oh, I couldn't wait to find out!

Tia was quite a babe indeed! She had black, middle length hair, in about the same hairstyle as Suguha, and blue eyes. She was wearing a blue, one piece, long sleeved summer dress and black sandals.

Asuna was wearing a red summer dress that left her shoulders and arms exposed and slippers the same color.

Suguha was morec casually dressed, with a white t shirt, blue shorts and flip flops.

I was wearing a white t shirt and green trousers.

For a while, we sat at the porch and discussed about non sexual stuff. Maybe Tia was not a slut after all. Maybe Suguha had invited us just to hang out.

NOT! Suddenly, a meaningful smile formed on Tia's face. 'By the way, are you up for a challenge, Kirito kun?'

Not bothering asking for further details, I instinctively snapped: 'We're on!' That was a little reckless of me, but I never back down from a challenge.

Tia stood up and motioned me to follow. I followed her in the house, Asuna and Suguha coming along.

To my surprise, we entered the bedroom. I noticed an unopened box of condoms on the drawer desk. Tia sat on the bed, untied and removed her sandals in an unbelievably sexy manner, and lay down in a lateral position. She gave me a seductive look.

'So this is what the challenge is about,' she began explaining. 'You and I shall have sex, as many times as possible. As you can see, there is a box of 12 condoms, so we won't run out. The first one to succumb to fatigue and admit they can not go on any further is the loser.'

I looked at Suguha and Asuna, who had sat on two stools in the meantime. 'I... I assume you girls won't participate,' I guessed.

'Of course not,' Suguha smiled smugly. 'This is a stamina contest between you and her. It would be unfair if we butted in and tired you out, thus giving my classmate an unfair advantage.'

'But don't worry about us, Kirito,' Asuna added with a smile. 'We will just sit here and look. We are content with that.'

Regaining my confidence, I turned to Tia. 'So you think you can beat me in a battle of this kind, silly, little girl?' I asked provocatively. 'I'm warning you, my personal record is 9 times in a row.' (see Chapter 26!)

'I think I can handle this,' she reciprocated the smile.

'Fine. This is your funeral,' I said as I approached.

I got on the bed. I kissed and groped the girl's feet, calves and shins, eliciting moans from her. Her skin was unbelievably soft and pleasant to touch.

Suddenly, I turned her over, eliciting a squeal. I raised her dresses skirt and groped her ass as I removed her underpants.

'No anal,' Tia turned her head to me and raised a finger. 'Vaginal sex only so that both my and your genitalia will receive the same amount of strain. I don't want to win thanks to an unfair advantage.'

'I congratulate you for the fair play, miss,' I winked. 'But you're still going down.'

With those words, I charged at her. Over the following minutes, we were wildly making out while stripping each other to nudity. Meanwhile, Suguha and Asuna were watching and rooting for Tia. (So you wanted the slut to win instead of your boyfriend, Asuna? Not very kind of you!)

We were now nude. My hands and lips were enjoying her breasts, which were smaller than Sugu's but awesome nonetheless, her belly, her neck, her thighs.

Tia turned us over so that she was now on top and started exploring my body. I enjoyed the sensation of her hands and lips, closing my eyes and moaning.

Eventually, she reached my penis. 'No blowjob either,' she winked at me. 'For fair play reasons.'

I chuckled, moved towards the desk, took a condom, put it on and got on top of her. We started thrusting, in missionary position.

'Come on, Tia. Beat this sucker,' Suguha cheered.

'We know you can do it, girl,' Asuna added.

Sometimes we were making out, sometimes we staring at each other and moaning, the girl's screams of pleasure getting louder and louder and, thus, making it more and more difficult for me to hear my sister and official girlfriend cheering.

Finally, we enjoyed an intense, simultaneous climax, at first screaming and then with our lips joined but still moaning.

We parted and collapsed next to each other, panting.

When we caught our breath, Tia removed the condom from my penis. 'Wait a minute,' she said sweetly. 'I'm going to the bathroom to toss it and then I'm coming back for the second round.'

I enjoyed a view of her rear side as she ran away. Oh, I couldn't wait! The first round had hardly tired me at all! The girl stood no chance.

For some reason, Sugu and Asuna burst into laughter at that point. I raised an eyebrow but decided to stay focused on the match.

Tia returned a few seconds later and got on the bed, on all fours. 'Come on, big guy,' she wiggled her hips. 'No rest. The challenge must go on. Fuck me, doggy style.'

No need for her to tell me twice! I got on my knees, put on another condom and shoved my dick in her vagina from behind, making her gasp.

I fucked her this way for a long time, holding her by the waist for balance, although sometimes, I would remove one hand and grope her back or ass or slap her on various parts of her rear side.

We kept fucking until it was dark outside. After every round, Tia would dash to the bathroom to toss the used condom before coming back for the next round.

We fucked cowgirl style, reverse cowgirl style, sideways and facing each other, sideways and with her back turned to me and, finally, with her legs on my shoulders.

After the seventh round, I felt drained, whereas Tia was obviously in a much better condition. As much as I hated it, I had to admit defeat.

'Congratulations,' I sighed, collapsing. 'You won.'

The three girls in the room burst into laughter. I sat up and gave them curious looks. What was going on?

'Come out, sis,' Tia called out. Another nude girl that looked exactly like Tia came out of the bathroom!

For a while, I would gape at the two identical girls, my eyes darting from one to the other. 'Kirito, meet my twin sister, Premiere,' Tia introduced us to each other.

'Hi,' Premiere raised a hand and greeted me.

'You fucked me 4 times and my sister 3 times,' Tia explained and shared a laugh with her twin.

I glared at Asuna and Suguha, who had burst into laughter as well. 'You knew this all along?' I cried.

The two girls nodded with mischievous expressions. I facepalmed. 'Okay, I admit I got tricked,' I sighed.

Suddenly, I got a playfully angry expression. 'But you'll pay for this,' I said and charged at Asuna and Suguha.

Without resisting, the two giggling girls let me force them to the floor and start undressing them while enjoying their bodies with my hands and lips.

By the time they were nude, though, I felt a pain in my crotch. 'Ouch,' I laughed. 'It's still too sore. Sorry, girls. I can't take revenge on you tonight.'

'Don't worry, Kirito. We will take revenge for you,' one of the twins said and beckoned to the other two nude girls to get on the bed.

'Just sit back and enjoy the show,' the other twin said.

I sat on the stool and started watching in awe the four nude girls making out on the bed.

Eventually, they started scissoring, in pairs, Asuna with one twin and Suguha with the other. I no longer know which twin was who and I didn't care either. I had officially died and gone to Heaven!