"Please, Donnie."
The clinking and clanks of the chains is a slow, steady throb at the back of his head. He wishes he could put his headphones on, but he can't run the risk of Leo escaping. So he has to sit, and listen, and pretend it's the chains that are really bothering him.
"Please fuck me."
He has to hold his hand steady before he pours the beaker to keep it from shaking. Leo doesn't say fuck, never has. And his voice has never been this low, this rough, this wanton. 
"I need it. You know I do. Can't you smell it?"
He can. The scent of desire hangs heavy in the air, rich and choking and so wonderful he thinks he might vomit. Just chemicals, he repeats to himself. Chemicals, manipulation. You're the one with the key to the chains. You are in control. 
"You can shove your nice, big cock down my throat and call me April. Wouldn't that be nice?"
"Shut up." Donnie checks his phone; where are those idiots with his ingredients? (Please let them okay, please let them not have left him here with this insanity, with these words that make him want to cut out his aching dick with a scalpel). "Please, just shut up." 
"You don't even have to let me out of these chains, you know. In fact, it's probably best if you keep me here." A soft giggle. "I've been very bad. I need some discipline to correct my wicked ways."
"You're not my brother." Donnie's fingers drum anxiously on his side as he paces, watching the mixture boil. "That fucking egg messed with your head, it--"
"Did it?" Leo the monster sounds genuinely surprised. "How? Haven't I always been the mama of the family? The one who watched over you, dried your tears, looked after your needs while Papa was gone?"
A soft chuckle. "You may be a big boy now, but that doesn't mean I stopped loving you. And now I can take care of your big-boy needs."
"I don't need anything from you except to get the fuck out of my brother." 
It doesn't even acknowledge that. "You know what I think, Donnie? I think you've been working too hard, stressing yourself out. You need to take a breather, blow off some steam. Something to help clear your head, you know?"
"Shut up shut up shut up--" He needs to get out of here, away from that smell, but he can't abandon his brother, can't risk him getting loose. He's pacing, trapped, the words slithering into his brain like snakes.
"You want to pin me against the wall, Donnie darling, and shove your big, throbbing cock up my nasty little ass, giving a thrashing I'll never forget, put your big tough leader in his place." He's never thought about that before, he hasn't, so why does it feel so good?
"--pump me full of cum until I'm fucking bulging, make me grow round with little genius babies so that you have a nice big ass to fuck. I'll never tease you, baby, you can have it whenever you want--"
"SHUT UP!" He's across the room before he can stop himself, slamming his brother against the wall. And oh god, that scent is so much sweeter and so much more terrible here, slamming into him like a sucker punch so that for a second all he can do is stare at Leo stupidly.
Leo smiles, sweet as poison, and sinks his teeth into Donnie's neck. They go crashing to the floor and Leo lets out a throbbing churr, grinding up against Donnie's crotch.
It's so fucking good , and Donnie can't even think enough to pull away. He just lies there, letting Leo pump venom through his skin, the world growing hazier by the second.
When Leo finally sits up, mouth dripping with blood, Donnie can't think of anything except how gorgeous those night-black eyes are. He runs his hands down Leo's shell, over his ass, squeezing and pulling while Leo moans at his touch.
"Please..." The words are coming from his own throat, and it's his own hands that are undoing Leo's chains. He wants to get lost in his brother's tight heat, to be ridden hard into the ground and scraped free of impurities.
"... fuck me."