"Artie?"
"Mmm?" She blinks, long and slow, like she's underwater. Only, she's been underwater and it's never quite this slow, or this warm, or...damp? She's feeling oddly sweaty right now, especially between her thighs. At least, she thinks it's sweat.
"Is everything okay?" A calloused hand rests on her cheek, thumbing running gently over her cheekbone. She leans into the touch almost automatically, shivering as cool breath blows over her face. "You seem kinda distracted."
"Mmm?" Artie peers into her sister's eyes--her big, glowing green eyes. "I'm fine, Sof, really. Just, I, uh...."
Sof chuckles, a warm hand wrapped around Artie's shell and pulling her close. She sucks in a breath at the scrape of her sister's scaly thighs against hers, the press of her big sister's plastron digging into her chest.
She can feel a heartbeat right now, pressed up against her, humming into her bones. It's Sof's same strong, steady pulse, but it's slow, somehow, with each other shuddering out a glacial place before subsiding into an unnaturally long gap. Or maybe is it just that everything feels slow to Artie right now?
"You know you can tell me anythin', right?" She can feel Sof's mask tails brushing lightly across her skin, soft as butterfly wings. "I know I ain't exactly, uh, approachable, but I'd never done nothin’ to hurt ya. If you really need be, I'll always be there."
"I know." She can't imagine a world where Sof would never come through for her. "Of course I know."
"But there's somethin' you ain't sayin', isn't there?" Sof's hand is rubbing up and down her shell, steady as a pendulum. "I think there are a lot of things you ain't tellin' me, baby sister." She wriggles her hips at the word baby and heat blooms between Artie's legs, making her squirm.
"Ain't that right?" Sof's voice sounds dark with amusement, smoke curling in her earslits and wrapping around her bones.
Artie laughs, high and nervous. "C'mon, Sof, y'know me. I'm an open book, remember?"
"I know that, darlin.'" Sof's tongue flicks against her neck, there and gone so fast Artie's not sure she didn't imagine it. "But everyone has secrets, you know? Keeps you from goin' nuts, having a little piece all ta yourself. I respect that."
Her fingers run through Artie's mask tails, scratching the back of Artie's neck in a way that makes her pulse stutter. "Thing is, I think some of the secrets you're keepin' close to that pretty chest a'yours have a lot to do with me, don't they? So, don't I have a right to know?"
"....About you?" Artie glances at Sof, then glances away, gaze sliding through the haze of the room around them. They're--where are they, again? "I, I don't know what you're talkin' about, si--" She yelps as she thuds onto her back, Sof's weight bearing down on her. Her sister's muscles press hard and tight against her sensitive scales and Artie moans. 
"Yeah," Sof's smiling, bright and beautiful and very, very sharp. "I think you've got quite a few little secrets, Artie." Her fingers slip between their bodies, dragging their ice-cold tips against Artie's stomach.
"I think," Sof purrs, "that there's a reason you're always so obsessed with buggin' me, watchin' me, rilin' up." She licks her lips, tongue brilliant red against green skin. "I think there's a reason you're always shakin' that cute little ass a'yours in my face all the fucking time. "  
Her wrist twists, palm shoving down between Artie's legs. Her fingers jab against Artie's folds, cold and mean and bullet-accurate, like she's been studying where to touch for years.
Artie helps, half out of shock and half out of bright, stunned pleasure. She wriggles back onto the bed, panting, trembling all over. Sof feels so, so heavy and Artie doesn't know how to get out from under her, even though she knows how to unbalance stronger opponents. Doesn't she?
"You gotta..." She licks her lips, head swimming. "You gotta, you gotta stop, Sof. It's, it's wrong, we're not--"
"No." Sof's voice rolls out, deep and dark and endless, rumbling painfully over Artie's scales. "No more lies, sis." She grabs Artie by the chin, fingers digging painfully into her flesh, and yanks her head up so that their eyes meet. "You know what you want, don't you?"
Artie stares up at her, into those endless green eyes swallowing up her little world like it's nothing at all. Sof is a light drawing her in, sucking her air away, and she's going to burn, she wants to burn.
"Yeah," she whispers, soft with hopelessness. feels something inside her start to fracture, pieces slipping through her hands. "I know."
Sof hums, brushing cool lips against hers. Her breath tastes of blood and torn meat; Artie needs to suck it down, to never breathe anything else for the rest of her life.
"How long?" Soph whispers. She rocks her hips, long and steady, and Artie sobs without knowing why.
"S-since thirteen," she grits out. "You were in the shower and, and you--" She thinks of Sof leaning against the bathroom wall, scowling as she scrubbed her thighs. Her muscles had already started to develop, the slightest motion taught with power, and her scowl made Artie's knees weak. "It was the first, the first time I ever really saw you. Like, I'd seen you before, but, but..."
She hiccups, breath hitching. "You were, you were shining. It was the water, I guess, but it wasn't just that, it was--" Sof's hips snap, sharp and vicious, and Artie yowls, shaking all over.
"Go on," Sof croons.
"You were." Tears sting her thighs, wetness on her face matching the terrible heat she feels sloshing in her guts. "You were beautiful, Sof. I'd never seen anything like it. I--" She flushes a painful red. "I touched myself for the first time that night, thinking of you."
"Oh, baby," Sof sighs. "I wish I coulda seen that. Wish I coulda taken pictures and hang them up everywhere, let the whole city know what a needy, dirty slut you were, even then." Artie flinches at that and Sof's face softens.
"It's all right," she murmurs. "Don't be shy, darling. You want to know something?" Sof tilts her head, needle-sharp teeth dragging across Artie's neck. It feels like a knife being held to Artie's flesh, a heartbeat away from cutting her open.
"I've got my own secrets." Sof's voice is sinking around her, into her, washing everything out to fill Artie up. "And one of them is that I've been thinkin' of doin' this every since I saw you bent over the kitchen counter when you were fifteen." She wriggles her hips with a low groan. "I wanted to walk right ova there and sink my teeth into your perky little ass."
Artie whimpers at that, thighs shuddering. She can feel more of Sof's fingers pushing her in, stuffing her full with terrible, beautiful things.
"I hated myself for that, for a long time," Sof whispers. "Do you?"
Artie squeezes her eyes shut, even though she can still see Sof's terrible emerald gaze blazing behind her lids. "It's wrong," she grits out. "It's wrong, Sofie--" She screams as all five fingers jab inside her and flex, lightning zinging toward your Zeins.
"No. More. Lies," Sof grits out, punctuating each word with a brutal snap of her hips. "I told you, little sister, I fucking told you" She rocks them both and force, faster and faster, sweat trickling down her face as her gaze singes Artie's scales. "No more secrets, no more hiding." 
"Sof," Artie forces out. "Sof, Sof, please--" She doesn't even know what she's begging for, but the desperation makes her voice tremble. "Sofie--" 
Her sister's lips crash against hers, teeth ripping her mouth open. Artie shrieks and it's not in pain, even as she feels the taste of death on her tongue. Her legs come up to wrap her sister's waist as she hangs for dear life.
Sof rips her head away, blood dripping from her mouth. "Fucking cum for me," she spits, and Artie does, shattering around her sister's hand like waves against a rock. She cries out so loud it makes her own head ring, the world flashing in and out of existence before her eyes.
Then she's falling back, slumped against the pillows with a sob. She feels Sof still looming over her, but she's pulled away, enough that Artie might be able to twist for an opening if she tried. Instead, she just lies there, gulping like a beached fish.
"Well, Artie." Her sister's damp fingers trail up her plastron, drumming lightly against her skin. "What do you want now? And remember, no more secrets."
Artie lets out a slow, rattling breath. Her eyes sharpen, dragging away enough from her sister's eyes to see her bloodied teeth, her cracked nails, her thighs slick with her own desire. She reaches out and takes Sof's hand, rubbing her thumb over the slow, steady pulse.
What does she want? Well, if she's really going to give Artie the truth.
"More," she says, looking back up into Sof's eyes. The green light tugs her and Artie can't remember ever wanting to do anything, but fall. "More, please." 
"Thought so." Sof smiles, teeth glinting like daggers in her mouth. "Good girl." And she falls on Artie like the oncoming night.