Disclaimer: I don't own anything.
Summary: Filled for this prompt here on the kink meme: Sherlock is possessed by some sort of demon. It is not an absolutely evil creature, but it is definitely twisted and wicked and damned.
John doesn't even notice the difference.
As the demon rifled through this man's (Sherlock, it picked up as it scanned through his memories. The demon had been around for thousands of years, but even it could admit that the name was fairly ridiculous) mind, it grinned. Oh, this was rich. Somehow it had just found the one person on Earth who was stupid enough to summon a demon by accident.
The demon surveyed the kitchen table, eyeing the rabbit's bone, the herbs, and the runes that had summoned it. According to Sherlock's memories it was an experiment of sorts. Amused, the demon looked at the paper cut on his current host's finger which was where the blood had come from to seal the deal.
Well, it said deal. A deal implied more of a symbiotic relationship, when this was more of a, well, parasitic sort of thing.
Understandably, Sherlock really wasn't pleased about having his body being taken over by a demonic being. The demon was rather surprised though; instead of pleading and begging like most did, this Sherlock bloke just mentally surveyed it, fascinated, and then began a tirade of some sort of logic drivel. Frankly, it was all giving the demon a headache.
It sighed, its voice coming out as a low baritone. "Do shut up," it said, rolling it's eyes. Sherlock, of course, didn't, and continued some sort of deduction about who and what the demon was. A tad ridiculous, as it was already well aware of that.
Still, his host's ranting was worth it when the demon was able to flex its fingers and enjoy the sensation of the movement. It grinned, and if anyone had seen Sherlock's face, they would have witnessed it twisting into a mischievous, yet not altogether unfamiliar, expression.
The demon bit his (or Sherlock's, whatever) lip as John entered the flat. This was always the hardest part. It could read its hosts thoughts and know every single thing about them, but the people closest to the host could generally tell if something was…off, about them. This had led to a few awkward moments in the demon's past, and it had been hoping this host would be better.
John made his way into the kitchen, and silently raised an eyebrow at the runes and blood on the table. The demon winced internally, not quite sure if it had an explanation for this, but before it could even open its mouth, John said, "Is this for the case?"
The demon blinked and nodded. Unbelievable. Blood, bones, and symbols of power were scattered on the kitchen table, and John Watson was acting as though it was the norm. The demon wondered if this sociopath had gotten himself an actual saint as a roommate.
You really are an imbecile, aren't you? Sherlock thought. Ah, so the host was testy once the subject of John Watson was brought up. The demon smiled smugly as Sherlock sulked in his corner of their shared body.
"What do these mean?" John asked, pointing at the symbols in curiosity, and unknowingly interrupting the conversation between the demon and Sherlock.
The demon mentally shook himself and began explaining the runes in far more detail than any human would be able to, but again, John didn't seem to find this at all odd. Fascinating.
The demon was performing a blood ritual when John next walked in on it. This time it really was sure it was screwed. It could only get away with so many "experiments" before John got suspicious, and even Sherlock was rolling his eyes at the situation. Silence, the demon growled internally, and Sherlock's thoughts miraculously (or not so) came to a halt for what was probably the first time in his life.
Amazingly enough, as opposed to John suspecting that his flatmate wasn't exactly human after all, the man just scowled. "If you stain the floor with that, Mrs. Hudson is going to kill us."
The demon stared at John Watson for almost a full minute before the doctor began to waver under its gaze. "What?" John asked.
Blinking, the demon looked away. Perhaps there was a good explanation for this. John Watson was obviously mentally deficient. The demon could feel Sherlock rolling his eyes at it and scowled. "Your whole species is completely idiotic," the demon muttered under its breath.
Instead of acting affronted, John laughed. "And what does that make you?"
The demon only smiled and continued with its ritual, painting the blood in slow, careful circles.
John opened the refrigerator and sighed. This, the demon thought, was surely it. The point where John would realize there was definitely something off about Sherlock.
And indeed, John looked at Sherlock and narrowed his eyes. The demon had practically resigned itself to a new body when John spoke up.
"Sherlock, do you really have to keep the body parts right next to the milk?"
The demon blinked. Well that was…unexpected. This John Watson was even more peculiar than it'd thought. Either that, or he was just mad. Both options were looking acceptable at this point.
It'd been a few days since the demon had borrowed the body of Sherlock Holmes, and not once had John been at all fazed by it. Any of it. Not the rituals, or the dead animals, or the complete disregard for humanity (this last one was treated with a sort of resigned exasperation rather than the usual disgust).
The thing that gave him away, in the end, was that he'd needed some pig's blood for another ritual, this one for more lucrative businesses (it'd been awhile since the demon had been able to get up a good soul trade, and it was quite pleased at the prospect of it).
Putting on Sherlock's coat, the demon called to John (because it just seemed like the sort of thing flatmates did), "Going to do some food shopping. Need anything while I'm out?"
It was the most innocent comment the demon had made all week, and yet it was the only one that made John's eyes narrow suspiciously. "What's wrong?" he said, voice tense.
The demon raised its eyebrow in confusion. "…nothing? I was only offering to do the shop."
This comment, even more innocent than the last, actually got the demon flattened against the wall by an irate looking John Watson. The demon's eyes widened in shock as it found its arms pinned against its back.
"And you and I both know that the one time you did the shopping, I ended up strapped to a bomb. You doing the shopping is never good. So tell me: what. Is. Wrong?" John said sharply.
The demon only looked at John for a moment. Sherlock's surprise was just as acute as its own, and underneath that the demon could sense a hint of pride. "You're not going to let this go, are you?" it asked, amazed at the two nutcases who resided in 221.
"Nope," John said, shaking his head.
The demon could only laugh at that. "Brilliant," it said, before it decided that while it was endlessly fascinating here, even the demon wasn't sure if it could handle the eccentric life of Sherlock Holmes and Dr. John Watson.
"A…a demon," John repeated slowly.
"Yes," Sherlock said through gritted teeth, stretching out his muscles. God, did it feel good to have his own body back again. "Amazing really, that you didn't notice a single thing off. Not the blood rituals, or the animal sacrifices, any of it."
"Oh, right, what normal human would draw runes or keep corpses in the refrigerator? Or have animal bodies around for 'experiments'? Oh wait, you," John said, rolling his eyes.
Sherlock sighed and flexed his fingers, relishing the small miracle of being able to operate his own body parts. He paused for a moment. "…You really didn't notice anything until it offered to do the shop?"
John shook his head. "Nope."
Sherlock probably should have been offended, but instead he found himself laughing. "Brilliant," he said softly.