I do not own Sword Art Online or anything related to Reki Kawahara and Studio A-1 Pictures. This story will be focused on the Kirigaya Siblings, Kazuto (Kirito) and Suguha (Leafa). Also, spoiler warning: M is in case of sexual themes and stuff. Anyway, other than that, enjoy!

Sword Art Online: Kirito X Leafa, The Kirigaya Sibling Affairs

Chapter 0: Prologue

January 15, 2027 – Nighttime

At the Kirigaya residence, where the Kirigaya siblings were living alone together with their parents away from work, Suguha Kirigaya, also known as Leafa in an online game called ALfheim Online, or ALO for short, was sleeping in her bed peacefully since it was the middle of the night, dressed in nothing but her white shirt that did little to hide her large round breasts and red and pink panties. Or rather, she was Full Diving into the virtual world of ALO with the AmuSphere, playing as her avatar, Leafa. And within the virtual world of ALfheim, Leafa was in her new private residential home residing in the Sylph's capital city Swilvane and was sleeping in her own queen-size bed. Or at least would be if not for the moans that were happening inside the house but could not be heard from the outside.

Ever since the incident regarding Sigurd trying to overthrow Sakuya through the Salamanders was resolved, as well as completing the quest to reach the top of the World Tree, before ALO was suspended and then bought by Company Ymir, Leafa had been rewarded to accept any request from her as thanks for putting a stop to Sigurd's plan and completing the World Tree Quest. Well, technically, it was her brother, Kazuto Kirigaya, A.K.A Kirito, who was the one that resolved them, but because Leafa was involved, she was allowed to accept any request she would be given as a reward for saving the Sylph and the Cait Sith Alliance from falling apart and completing the World Tree Quest. And Leafa's request…was to have a new residential home, and her new residential home was comfy, homey, secure, and perfect, where it was completely private for herself, completely protected and soundproof, so that no one, not even her player friend Recon, would dare to come and bother her when she was doing something that was…private and personal. Speaking of private and personal, Leafa was dressed in her green silky pajamas, saved for the bra that was removed and laid on the ground, and was lying on her bed and moaning loudly as she was masturbating, as she was rubbing her pussy with one hand while massaging one of her naked breasts with the other while pinching and tweaking her nipple.

"Oh…thank God my new place is private and completely soundproof…" Leafa thought while moaning loudly, "It would've been really…really bad if anyone saw…or even heard me…ah…e-especially if it's…it's…"

"O-Onii…Onii-chan…!" Leafa moaned out loudly, as she rubbed on her already wet pussy from the constant masturbating and pinched her nipple a bit harder, all while thinking about the one person that she was masturbating to; her brother, Kirito.

For those who don't already know, Leafa, or rather Suguha Kirigaya, was in love with her own brother Kazuto; ever since the SAO Incident, her feelings for her brother started to grow as she began to see Kazuto not as a brother, but as a man worth falling in love with. At first, she felt guilty about having these feelings, even felt disgusted with herself about having these feelings, but as time passed, and after learning about the truth of them being cousins, Suguha began to consider the idea of maybe, just maybe, being with Kazuto together as lovers once he was free from SAO, before burying her feelings for him for that time to come. However, after learning the truth about Asuna Yuuki, A.K.A. Asuna, being Kazuto's in-game wife and real-life girlfriend, Suguha decided to completely bury her feelings for her brother completely so that the two of them could find happiness together, even after learning the truth that Kirito and Kazuto were the same person, and eventually even saving Asuna and the other 300 trapped SAO Survivors. However, even there was so much to how long her feelings could remain buried for so long, and there was so much to how Suguha could take it, even now as Leafa.

"Onii-chan…Onii-chan…Onii-chan…!" Leafa moaned loudly while rubbing her pussy much harder and much quicker than before. She was rubbing herself much harder as she was imagining being with her brother and having sex with him while he was touching her. It was getting much harder for her to hold herself back as her buried feelings continued to resurface. And it was all because of the man that she was in love with, the man she still has feelings for: Kirito.

After spending so much time with her brother in ALO, going through and clearing out so many quests together, within the Aincrad Castle or otherwise, sometimes even with the others joining them, especially with the new addition to the team Shino Asada, A.K.A. Sinon, Leafa's feelings for her brother continued to grow larger and larger, making it harder and harder for Leafa to keep it under controlled and keep buried deep inside her. And what she was doing now, masturbating to the thought of having sex and doing naughty things with her brother did nothing to dwindle her feelings for him. Instead, it was only making it worse than it already has.

"Onii-chan…ONII-CHAN!" Leafa moaned much louder than she had, as she was rubbing onto her pussy much faster and much harder, as well as pinching and tweaking her nipple much harder, as she imagined her brother, her Kazuto, going and moving inside of her much faster and much harder than before until finally. he came inside of her. "Oh…fuck…oh, fuck…FUCK…KIRITOOOOO!" Leafa screamed out loud as she finally came from that thought alone, and her body began twitching and convulsing so much as she arched her back and her pussy began to spray out juice onto her bed. Once her orgasm had passed, she landed her back on her bed and laid her head to her left as she began panting to try and catch her breath.

"Oh…my God…" Leafa panted, "This is…about the 35th…time…I did this…" She looked up at the ceiling and said, "It's a good thing that…I got this place for myself…so that I wouldn't have to do it in…real life…I'd be embarrassed if Kazuto found me doing this…in real life and in my room…"

Yes, Suguha Kirigaya has been doing this for some time since her feelings were growing, in the virtual world as Leafa. Now, granted, she would've done what she was doing now in real life if she wanted to since her brother was out of the house and out of town for a while and wouldn't be back for a long time, However, Suguha didn't want to take any risk or wanting Kazuto to find out what she did, so she logged into ALO as Leafa and continued on masturbating to the thought of her brother.

Still tired from her masturbation session, Leafa covered her eyes with her right arm and sighed, and said to herself, "If only I…I could go and date my brother…if only Onii-chan would choose to date me…if only we could get married, then…we could've had sex with each other without a care in the world…if only…if only we weren't siblings…"

That was what Leafa-no, Suguha Kirigaya had desired the most: to be with her brother not as his sister, but as his lover. Granted, they were technically cousins, and Japanese Law does allow for cousins to marry one another and make a family with each other, so Kazuto and Suguha could marry each other without any issue. Only the issue, however, was that since Kazuto was adopted into the Kirigaya family, which was her family, it was not, or rather, no longer the case. Because of that, because they were marked as siblings on paper, they could not marry each other even if they wanted to. Another problem also lies with Kirito's love interest in both the real and the virtual world: Asuna. Because of their involvement with each other in SAO, the two have them have been dating each other for a long while, and while Leafa did what she could to support them, she also couldn't help but be jealous of Asuna because she had gotten to her brother first before she could, and it only frustrated Leafa more.

"Dammit…" Leafa grumbled, "If…if only I'd gotten to Onii-chan…to Kazuto-kun sooner…then…"

With a sigh, Leafa slowly got herself up off her bed and looked down a bit. and saw the mess that she had made on her bed, the sweat that she had made while masturbating, and the juices that were soaked on the mattress during her orgasm, before she looked at her wet fingers that she had used to masturbate herself with, its sticky wet fluids still covered in her hand, before she went and tasted herself, making herself moan in the process. But Leafa sighed again as she knew that her masturbation session was not enough anymore. In fact, it was never enough to satisfy her anymore as her feelings for her brother kept on growing and growing. And Leafa knew if this kept on going, she wouldn't be able to take it anymore.

"I…I can't…I can't take it anymore…!" said Leafa, as she was covering herself, "I-I know we're siblings, but…I just…I can't take it anymore! This isn't satisfying anymore! I don't wanna masturbate anymore! I know we're siblings, but I…I wanna have sex with him! But…how…?"

Then, Leafa remembered that tomorrow morning, she and Kazuto would be going out shopping for new clothes together in the real world, just the two of them together. Which meant that Leafa, as Suguha, could have Kazuto all to herself, and without anyone else interfering since they'll be busy doing their own stuff in real life, especially Asuna who will be going on her away trip with her family. Which meant that this could be Suguha's chance to have sex with Kazuto and make him hers. They just needed to go someplace where they could both be alone and not at home where their parents would likely be when they get home from work early, most likely a love hotel where they could then make love with one another, where they could have their little secret affairs with each other. If she could do that, then…

"Yes…" Leafa thought to herself, "I can…I can do this…I can make Onii-chan-No, Kazuto-kun mine! No, I will make Kazuto-kun mine! I mean, there's no way I could make Kazuto-kun break up with Asuna-san, not completely, but I can at least keep him to myself and make him mine and have sex with him in secret, especially away from our friends and family. Yeah. I can do that!"

With that plan in mind, Leafa decided that once she logs off and goes back into the real world as Suguha, she will do what she has planned for tomorrow morning. She just needed to wear something that may entice Kazuto and then buy some sexy clothes that might just arouse him, so much so that he might want her so badly that he comes at her and have his way with her completely. Oh, that thought turned Leafa on so much, and she began to masturbate again to that thought and to her plan on seducing him, and throughout the night, Leafa would moan out, "Onii-chan…Kazuto-kun…Kazuto-kun…Kazuto-kun…!"

And thus, this was the beginning of her plan to have her sexual affairs with her brother, her Kazuto.

So, what do you guys think? Please, be sure to leave a review for me on what you guys think of the story! I hoped you all enjoyed it. Don't be shy and don't just read the story, REVIEW and tell me what are your thoughts of the story!