This is indeed based off of Sword Art Online's ALfheim Online (or, literally, Land of the Fairies/Light Elves).

Disclaimer: I don't own Sherlock or the original ALfheim.

Summary: John thinks that, to curb Sherlock's boredom, a virtual reality game may be of help. He obtains the Nervegear game systems for the both of them and buys ALfheim Online, a game that claims that players feel as if they're flying. Soon, cases in real life become intertwined with the game, all stemming to protect the dark truth underneath ALO. Sorta fantasy AU Case!fic

Prologue: Finding One's Wings

"John, what the bloody hell is this?"

John glanced up at Sherlock from over the pages of the book he was reading, raising an eyebrow, "What's what?"

"This." The younger man held up a black helmet-like device strapped into the wall.

"That," John replied, mocking his annoyed tone, "is the new cure for your boredom."

Sherlock let out a long suffering whine, "Joooooooohn, this does nothing for me!"

"Not like that, it doesn't. It's a virtual reality helmet, called Nervegear." John explained, plucking the helmet out of the detective's hands. "Using this system to play a game, you fully immerse yourself into the game. Your body will be here in real life, but your mind will be sent elsewhere."

That got Sherlock's attention.

"I actually have a game for us to play," John gave the helmet back to the detective, rummaging in another box depicting another of the Nervegears before taking out a game with the image of two fairies on the cover, "ALfheim Online."

"Land of the Fairies?" Sherlock raised an eyebrow, "Why something like this?"

"They say that you can actually fly in this game. Get the feeling of it and everything." John said, excitement glittering in his eyes.

Sherlock decided that this would be at least mildly interesting. It would definitely give him something to do until the next case appeared. So, he resolutely laid down on the couch and put the so called Nervegear on, feeling as if he looked a little foolish. John grinned and started to leave the room, "I already put your copy of the game in. Just activate the system!"

He could hear John's footsteps retreating. Seeing as the helmet had no visible switch and with the microphone attached, he assumed that it had voice activation. "System, activate."

There was such a bright flash of white that the young man had to close his eyes. When the light began to recede he opened his eyes. What he was met with took him by surprise. He could feel himself back on his couch in his flat, yet he seemed to be walking on a rippling black floor littered with stars.

"Welcome," A pleasant female voice greeted, "to ALfheim Online. Please choose your race and username."

Nine avatars appeared in front of him; all animated looking versions of himself in different forms with wings and pointed ears. Sherlock supposed that the gear had a sort of full body scanner. Interesting.

The first avatar seemed so ridiculous, he had to snort. It was a brunette version of himself with yellow wings and, strangely enough, cat ears and a tail. It was labeled Cait Sith, a sort of beast tamer race. The skill seemed to be fairly useless to him.

The next avatar was labeled with Undine underneath, a version of himself with blue hair. It was a sort of water affinity fairy with extremely powerful magic ability. This would definitely be appealing to a Dr. Watson.

Meanwhile, John looked at the avatar of himself in a blue cloak and with blue wings. It was perfect! To be able to heal and still battle underwater would be a wonderful experience.

He went through five other races that held absolutely no appeal to him before he saw one that caught his eye. Spriggan, styled in black. Their affinity seemed to be illusion magic and treasure hunting. While the treasure hunting didn't particularly seem interesting, it would no doubt come in handy when gaining money to obtain weapons and other such necessities. The illusion magic was what really intrigued him.

And, of course, there were no silly hair colors or extra features to it. He would just look like himself with elfin ears and black wings.

He reached out a hand and touched the avatar. A text box appeared, asking for a username. The detective, who had never seen the need for false names unless on a case, said, "Sherlock."

"Thank you for playing! Enjoy your time."

There was blinding white light and Sherlock Holmes blacked out for a moment. When he gained his bearings, he noticed two things. He was above a forest.

And he was very quickly plummeting towards the ground.

Sherlock barely had time to react as he fell. Not many things could catch him by surprise, but how could he react when the scene had so suddenly changed to his own crash-site? He finally dropped on to the ground, bracing himself with his arms and knees. There was a very unusual ache in his shoulder blades and his ears still rang with the sound of snapping branches.

Looking over to his left, he could see someone else. He almost couldn't recognize who it was, gaze lingering on the elfin ears and the very light hair that shone a pale cerulean in the right light. Only when he looked at the man's face and caught sight of the sky blue eyes did he realize who it was, "John?"

John snorted, smoothing the wrinkles in his blue cloak, "You couldn't recognize me. I don't blame you, Sherlock; I mean my hair is bloody blue for Christ's sake!" Sherlock got up and looked down at himself. He was wearing a black coat of sorts, the collar of which was already popped up. On the belt were the hilts of several blades.

"If you're wondering," John continued, "you look the same. Just with pointy ears."

"And if you're wondering, your hair is still blonde. It's just very, very light." Sherlock shrugged. He looked around. On either side of them was forest. "Where the hell are we?"

"I have no clue," John said, sighing a little, "It would be so bloody easy if we could just have a map of sorts…"

Sherlock thought for a moment, "Do you know how to activate the wings? The game did claim that players could fly…" If he could fly up high enough, perhaps he could see the rest of ALfheim.

"Oh!" John brightened, giving a smug look that showed that he knew something that Sherlock didn't, "It's quite simple, really. Just think of your wings appearing and use the muscles in your back."

Sherlock blinked and closed his eyes, concentrating. He could feel a small, paper thin something brushing his back and spreading out. When he looked again, he could feel wings fluttering with each ripple of his flesh. John gaped, looking awestruck.

"Oh."

Sherlock looked bloody magnificent. Large opaque wings the color of dusk protruded from his black coat, detailed with midnight blue. His pointed ears (which, John would later deny thinking) made him look adorable; almost boyish. His quicksilver eyes were catching the dim light of the moon as they focused on his wings, then on John himself.

Sherlock looked at him expectantly and he shook himself. He focused and could see the tips of blue wings brush his cheek. "Would you like to lead?"

Sherlock nodded and slowly began to ascend into the air. He paused, eyes going wide with wonder. He looked down at his feet, then back to John. His flatmate gave an encouraging smile. Sherlock looked up and shot into the air.

He had to laugh out loud. The feeling of the sky pressed against him as he flew was simply amazing. He could still, if he concentrated enough, feel himself laying on the couch back at his flat in London, but why bother? It's not as if he could do this in real life. Maybe John had made the right call with this game.

Then John was there, shooting past him and going higher before abruptly stopping. His flatmate looked back at him, seeming disappointed. His wings had begun to sparkle. Fairy dust, Sherlock absentmindedly thought.

"I suppose this is the flight limit…" John sighed. Sherlock frowned at that and flew beside him. The Holmes could see the twinkles of his own wings and his frown deepened.

It wasn't in his nature to give up that easily.

Sherlock focused on going higher, going above and beyond. That's when he began to push up and ascend higher.

This time, flying was an exhausting struggle, not at all pleasurable as he fought against some invisible bonds to go higher. When at last he felt that he could go no further, he looked down.

Just as he suspected, instead of clouds, there was the whole of ALfheim, spread out like map. They had come from the woods near the Sylph territory, it seems. They could take the mountain passes to the wetlands that would welcome John or go straight past the mammoth white structure in the center of it all to reach the ruins that would be his home. He looked at the white structure and the name: World Tree.

Before he could realize, he was plummeting again.

This time, John was there to catch him, beating his wings furiously. "Bloody hell, Sherlock! You're heavy!"

Once they both landed on the ground, Sherlock told him of his findings. John had grinned tiredly. "Maybe we'll explore tomorrow. It's getting fairly late."

Was it? Sherlock opened up the menu and stared at the time. They had been doing this for two hours. "I suppose so. There's always tomorrow, right?"

Sherlock and John both logged out. The detective was blinded for a moment with white light. When it faded, he could see the shot up ceiling of his flat. He blinked.

Well, things were just going to get more interesting.