AN: So I was tumbr-ing one day and came across this post - post/1095602608/sherlock-demonized

and someone had said how they'd like a fic about it, so I tried it out :D I've never really written Sherlock before, so this was my first try and I'm pretty happy with it. I tried to explain Sherlock with it, but I've no idea how it turned out. That, and I realise now, it doesn't mention Mycroft, oh dear. But I hope you enjoy it! Reviews on how to improve would be awesome :D

note - human thoughts are in italics, the demon's in bold

DISCLAIMER: Sherlock isn't mine ahhh, and neither was the GIF, I was inspired heheh

It was there, in the back of his mind, Sherlock could feel it. The smooth, silky voice, the demon, it was there in his mind. It always had been. It had come to him as a child, when he was sitting alone in the park. He was alone that afternoon, as he was most afternoons; alone and lonely. It had come to him and offered him something, offered him the ability to turn a blind eye to the loneliness, to the sadness. It said it could help get rid of the feelings, and a willing young Sherlock Holmes agreed. But there was a price.

The demon was dying, and it needed life. It needed a host, a body to live off, and Sherlock was the perfect applicant. So it was there, inside him, every day, for the rest of his life. Hiding the feelings Sherlock had hated so much, and the ones he hadn't minded. In fact all his feelings, every emotion, was suddenly gone. He could no longer feel any love for his brother, he no longer found joy in art. If had could have, he would've been scared.

So it sat there, it lived there, somewhere in that great mind of his, and it fed off him. It grew stronger each day, it learnt each day. It saw what he saw, knew what he knew. It gradually spread, not allowing Sherlock to limit it to his mind, but it reached out and went for more. The first time it seized control, he had been alone in his room, only a teenager at the time.

It took him and shoved him into the tiny corner of his mind, as it stretched its new limbs and grinned wolfishly at itself in the mirror. "My, my," it said in his voice, in Sherlock's voice. "What a nice change," it said. In the demons place, Sherlock found the feelings it had stolen, and for the first time in a long time, Sherlock was scared. He couldn't call out, he couldn't move, as the demon admired itself. But the demon was not that strong yet, and so it flickered, and then it lost control. Suddenly Sherlock was flung back into his body, and the relief vanished once more.

It would not try to do it often, but the demon tried to again and again, and every time, Sherlock got ahold of his emotions and he was scared. The thing had longer in his body each time, it held onto his body more and more. He tried to fight it some times, when he felt it rising, when his body froze and the demon rose, it pushed him back and filled his body. Some times, he tried to use his emotions against it, to see if he could at least carry his emotions back with him when the demon finally lost control.

While it grew stronger, in some ways so did he. He found small ways to poke at it, to pick at it while it held his body hostage. Sometimes, he would flicker into life again, emotions in tow, other times the two of them would be locked in a battle of the minds, and when Sherlock woke the next morning, he would find himself bruised and battered from the war that had waged.

It continued through Sherlock's life, up until now, this cool evening in 221B Baker Street. He had made a career for himself, one that didn't require him to work set hours, one that didn't have set hours because it was impossibly to predict when the demon would take him. He had even found one person to live with him; John Watson.

He hadn't really the feelings to regard him as friend, but when the demon did take over, Sherlock found that his emotions were notably different around John Watson. When he changed during the night, he would worry for John's safety, he found himself scared it might hurt him. He found himself caring a lot about the short man who had come into his life. In those few hours he would find himself wishing he could properly explain this to John in his normal hours, but back in his body he couldn't find the words to explain it. That made him sad (when he could be), the thought that John probably thought he was a heartless man.

Back to the night at hand though, and Sherlock was resting on the sofa, eyes closed as he lay, deep in thought. They were on a case together, and while John sat on the laptop, probably blogging, or maybe looking something up, Sherlock's mind was working at top speed, turning the facts over and over until he came up with the answer.

Without warning though, his mind stopped. He felt a flicker, and went to sit up, but he couldn't. This was bad, very bad. Nobody else had ever been around when the demon took over. Especially not John.

"No," he told it. "You're not doing this now," he told it, but it wouldn't listen. It poked at it's corner of the mind, and Sherlock let out a gasp. From across the room, John looked up over his laptop.

"Sherlock? You found something?" he asked. No reply. Typical, he thought and rolled his eyes.

Sherlock wanted to reply, wanted to tell John to get out, but he was frozen. He had to concentrate on stopping the thing as it clawed at his pitiful defenses.

"Oh, is someone worried about their little boyfriend finding out?" it chided, and Sherlock recoiled. Was he? No, he was more worried that -

"That I'll hurt him? Oh, well I hadn't thought of that, but…" it laughed, and Sherlock gasped again, as the demon broke through. He could feel his control slipping, again. John glanced up, a frown on his face.

"Really, Sherlock, if you've got something to say, say it," he said, getting up and moving closer to the man on the sofa.

"Not now John… don't… go away," he tried to say, but the words got no further than his mind.

John looked down at Sherlock, who lay stiff, his eyes closed tight. He was eerily still, he hardly seemed to be breathing. John inched closer, curious.

"Sherlock?"

Suddenly, Sherlock jumped, like a wave rolling through him. His eyes snapped open, and for an instant, John thought he saw something in them, something… scared? Then a darkness consumed the mans eyes, and he bolted upright.

"Hello… John," it said.

Sherlock could do nothing but scream.