prompt
Stanford era, Brady's POV as the demon inside him controls his body, takes over his life and tries to manipulate Sam
It had started with a slip of the tongue, the slightest change in tone and something slithering in his thoughts like oil, heavy and suffocating. See you later became see you at 10 and Brady had some intention of doing something. There was a purpose to the words now, but as Brady tried to focus on it, it fell away like water and left Brady feeling like he was missing something, watching Sam's retreating back as he ascended the stairs to the house.
The second time, it was his body that betrayed him. He had found the knife under Sam's pillow when he was visiting and he was going to put it back, he was, but the same black, oily substance slid over his body and cold metal pressed against his back as he slid it in his jeans. Brady tried to fight it, it was wrong for Sam to have a knife but it was even more wrong for Brady to take it from him if the guy was a bit paranoid. The oily thing slid over his thoughts now, soothing and whispering that it was all right, everything would be fine in the end. Brady kept the knife.
The small instances kept piling up. Brady was constantly paranoid that he'd do something to hurt Sam eventually, since he could lose control at any time. He tried to stay away from Sam and break off the friendship, but the thing made his legs move forward to sit beside Sam and forced his voice to be amiable and friendly. Brady felt like he was under an invisible guillotine, threatened by something that wasn't even there, so he did what the thing was wordlessly demanding and kept his friendship up with Sam.
The glass wall appeared two months in. Sam was visiting his house and suddenly Brady felt the familiar oily slide over his thoughts and body, but this time he was pulling the knife from his waistband and making a cut on his wrist. Red bloomed from it and he held his wrist out to Sam, who looked confused and a bit scared, backing away from him. Sam was saying something about that was his knife, and Brady what are you doing, but the thing was controlling him and Brady was watching from behind a glass wall. He was holding his wrist out, pleading, asking, enticing Sam to drink his blood. Demon blood, he called it. Sam said he wasn't a vampire, that this was wrong, but the night ended with not-Brady's wrist pressed against Sam's lips forcefully before pulling away, only for Sam to pull it back and a satisfied smile forming on not-Brady's face.
After the demon blood incident, Brady started learning names. Names of everyone who stopped by Sam's house when Jess wasn't there, while Brady was almost getting used to the flash of black in their eyes and the red circling Sam's mouth. Not-Brady was certainly satisfied, because Brady could feel his satisfaction slithering through his mind beyond the wall, a small smirk on his face and his blood on Sam's face almost as much as the other demons' blood. Brady was helpless to do anything but watch; he'd tried slamming on the wall and he'd ended up spending a week drowning in his own mind. He learned that it was a courtesy that the thing even let him stay awake.
It took three months after the wall formed for Brady's vision to narrow. Not-Brady was feeding Sam the blood almost constantly now; they had been training his powers for the past four weeks and Sam's appetite was increasing constantly. The thing - no, the demon, Brady had learned - was keeping his body alive, but Brady was suffering behind the wall; he spent most of his time dizzy and lightheaded from lack of blood, barely aware of himself, let alone the demon possessing him. He thought that maybe dying would be better than spending his life trapped in his own mind.
Nine months, and Brady was dying. He knew enough about himself that he was losing too much blood, too quickly, and his body wasn't going to be able to hold out much longer. The demon knew it, too, the oily slide slow and lethargic beyond the wall. Sam didn't only drink the blood; he was taking a little bit of the demon's essence with it, infused into the vessel's blood, and he had been taking it constantly from this demon for all eight months. Brady tried talking to the demon, telling him that they were both going to die if it kept this up, but it only whispered soothing, wordless things to him until he slipped beneath the waves. His last thought before he drowned was that the demon was willing to die for Sam, to reach that goal Brady always sensed beyond the wall, and neither of them were making it out of this alive.
Twelve months, and Brady was pulled from the ice-cold water, once again seeing from behind the mental wall. The demon's substance was like smoke, wispy in his consciousness, but there was that same sense of more that made it motivated to keep going, to reach that goal it wanted so desperately. They weren't anywhere Brady knew; it was dark and cold, lit by torchlight, and the surroundings were unfamiliar. They were moving fast, Sam ahead of them, but he was wearing something unfamiliar and he radiated power. His movements were graceful, fluid; predatory, Brady thought suddenly. They turned a corner and through the blur of his vision, Brady thought he saw a throne, someone unfamiliar sitting on it. Contempt flooded through the demon and, by extension, Brady, until it changed to satisfaction and he felt both of them fading again. He saw Sam in front of them; turning, sitting on the throne, blood splattered on his clothes; and then they were kneeling and fading fast. Brady yelled at the demon, telling him that they were going to die, but he felt the black waves lapping over his words and the same soothing, wordless nothings that the demon was whispering to him. He panicked; the waves were like oil, heavy and suffocating and Brady knew he was really going to drown this time. The demon ignored him, shoving him under the waves even as he went down himself, and Brady heard someone talking before the world went black.
"How may we serve you, my King?"