Note: Vampires. For anon who wanted possessive Rivaille. Part 1/2.

There is something sucking on his neck. Two sharp indents where teeth lie. Eren can't move his arms. Like something heavy is pressing him down, an invisible spell that brushes against his eyelids, whispers sleep, sleep. The voice is alluring, as all dreams are, as all dreams should be. But Eren grew up with the indent of a gun pressed in his palm for comfort, with the weight of stakes in his belt, and the most seductive thing in the world is death to those fucking leeches.

The vampire wills Eren to sleep, to close his eyes, to forget about the world and remember all things lost in dreams. The monster wills Eren to 'forget about the gun, forfeit your life, don't pick up the gun. Eren does it anyways, forcing his arms to move, shoves a fist in the thing's face, and as it falls down he presses the gun to its head and pulls the trigger. The bullets burn it instantly, sends it screaming back to hell from which he crawled. Its blood stains Eren's clothes, his hand, and he drops the weapon, climbs off.

It is harder to breathe. It doesn't matter. He brought the thing down with him. Another count, another death, another victory, however small. Eren's neck stings. He closes his eyes, forgets about the gun, forgets about his life, and falls asleep.

He shouldn't wake up.

He does anyways. It is a dry bitter wakefulness, the kind that leaves you chained to the wall, the kind that burns your throat, the kind that kills you (but you were never good at staying down, were you, now you wish you were).Eren leans forward and the chains electrocute him immediately. He flinches, back slamming against the wall and throat stinging with thirst. With abominations. The chains are heavy on his wrist as Eren lifts a shaky pale hand to his neck. It is smooth, no track of bite marks, only a dull cursed pulse. He's too thirsty to think of much else but he recognizes the cool bite of the concrete surrounding him, can taste the barrier of blood in the air.

He probably helped set it up. Before. Eren quirks his head as he hears a whisper of voices in the other room, it gets louder as he focuses. And the voices are familiar.

"Hm," Hanji hums, "we haven't known him long but even we could tell the determination he had to exterminate them. He lived off that." A whisper of papers being brushed aside, a click of a tongue. "I checked his files. Apparently he lost his mother to a vampire at a young age. He loathes them as easily as he breathes."

Hanji sighs. "Turning into something that you hate, well, I can't say it helps the boy's self esteem."

Someone else speaks up, but Eren can't listen, allured by the beat of a living heart. He can hear the blood in the veins, something warm and inviting, just a few rooms away. His tongue darts out to lick his dry lips. Just a sip, just a small taste, he's sure they are kind enough for that. Eren reaches outside and the chains respond in kind, electrocuting him.

"Fuck," Eren mutters, head collapsing back against the wall. What, he thinks, glancing at his palm, what was I about to do? The ache still burns live in his throat, a thirst he cannot tolerate. Look at you, something singsin his ear, a disgusting leech. You were never a human to begin with.

The boy starts, fingers stabbing to his throat, and the pain claws away the thirst if only for a little while. Shut up, shut up, shut up, he chants in his mind, stab, stab, stab. He stills eventually, watches as red drips down his fingers.

Rivaille visits him, standing outside his cage with a bland expression. He notices the blood dried on the dingy floor immediately, narrows his eyes. Eren lies on his back, not bothering to look up.

"Does this disgust you?" Eren mocks, carving fingers into his neck that leave long bloody gouges. Like he can scratch out that dull ache lying in the back of his throat, destroy that thirst he loathes if he just reaches far enough. The vampire closes his eyes, laughing drily. "I understand."

"It seems it sharpened your tongue too," Rivaille says. "You forget who you're talking to."

Eren sits up then, a painful languid wakening that rattles his chains. He leans forward, the movement shadowing his eyes, breathing heavily. He looks up after a few seconds. Rivaille regards the stare evenly, doesn't react when the bright color stains crimson.

"I'm sorry, corporal," Eren says, and the word might have sounded pleasant any other day. Rivaille says nothing, enters the barrier as if Eren weren't a threat at all. Eren swallows, looks away. The hunter rolls up the cuff of his right sleeve, stands before Eren's form.

"Drink," Rivaille says, presenting his bare wrist. They had said the boy wasn't completely stupid. Eren grabs the wrist, pulls down with inhuman speed to straddle him. The hunter says nothing when the vampire snatches the gun from his holster, presses it against Rivaille's forehead. The chain bites into Eren's wrists, but he ignores it.

"It's meant for vampires, but a bullet is a bullet," Eren preens, and if his fingers shake it's nothing to do with him. "I can hear your heart." A strong steady beat, even when Eren's face contorts into something hideous and raw, and his finger curls around the trigger. Eren stares down at Rivaille, with his dark dull eyes and his dark dull expression, and grows cold. His teeth split into his bottom lip as he fights the instinct to devour, and he curses, throws his hand up to press the gun against his own head, pulls the trigger.

It's empty, Eren thinks as the hunter throws him off easily, slams him into the ground. The chains stretch and send electric shocks through his body in kind. Rivaille shoves his forearm into the boy's mouth and Eren's teeth sink in immediately.

"Studying your body, finding its weaknesses," Rivaille observes, "using its strengths. Just some examples as to how this will be useful. There's nothing to do with a dead leech but burn." Eren's eyes are closed tightly, but the words singe in his mind. Eventually, Eren jerks his face away from the hunter's arm, teeth aching.

"I'll be in charge of you," Rivaille says, wiping the blood dripping from his arm with a towel, stares at Eren's bloody face. He throws the towel on the Eren's face, turns away with a curt 'clean yourself up'. Eren snatches the towel in one fist and as the corporal leaves, they both can't fight the strong urge to burn their skin off, just to forget the feeling.

Eren becomes more acquainted with Hanji as the days tick by. Rivaille's squad, if he's lucky, but everyone knows Eren will never step outside the barrier, the cage again. Not with his head intact. Hanji kneels next to him, throat stretched bare, examining Eren closely.

"Are you hungry?" Hanji queries. Rivaille shifts from his slouch on the other side of the room.

"No," Eren bites out, and Hanji shrugs. "I don't mind. You've been so accustomed to Rivaille's blood, might not be good for you."

"Not the neck, dumbass," Rivaille speaks up as Hanji starts to move, "one clumsy chomp, and you're dead."

"If he bites off my hand, that might be worse," Hanji replies, and Eren glances up to see dark dull eyes. Looks away.

"Not hungry," he repeats firmly as his throat burns.

"You're getting a little attached," Hanji comments casually. "Careful now." Rivaille scoffs. Eren is his responsibility, that is all.

A hunter from a foreign division finds Eren one day. As to why the idiot thinks that he needs to be involved when the vampire is clearly in control and chained is beyond him. Eren's strong enough to fight him off in close proximity. The problem is: the vampire won't.

Rivaille shoots the man through the head just as the bullet stabs into Eren's shoulder. Eren manages to press a hand against the bullet wound harder. It helps the poisoning, triggers Eren's face to contort, teeth to sharpen; eventually it will send the vampire off to die in its true form. Except Rivaille pushes his hand aside, digs into his shoulder to retrieve the bullet. Eren chokes as the bullet is removed, jumps up after Rivaille in response, but the chains send him slamming back into the wall.

Eren's losing too much blood, Rivaille observes as the beast like qualities dull again. Rivaille crushes the crumpled bullet in his hand and kneels before Eren. The blood clings to his pants he notes in disgust.

"If you cared about me," Eren mutters, eyes hooded as a bright crimson bleeds into them. "You'd kill me." Rivaille grabs the boy's hair, shoves Eren's face in his neck and the boy closes his eyes, tired.

"Don't be an imbecile," Rivaille says as Eren bites into his own lip stubbornly."I don't care for you at all." Eren sighs into his neck then, teeth pressing against the skin. Rivaille moves the boy's head to a more comfortable position as he drinks reluctantly.

Eren is his responsibility. That is all.