There is something unique about the scent of a fearful human freshly ripped open, an aroma you never quite manage to find anywhere else. It is heady and off-putting all at once, enough to make Raph if he breathes too deep, lights flickering before his eyes. 
Good thing he doesn't really breathe anymore. 
He and Leo kneel like penitents over the night's kill, bones twisting and snapping between their teeth as they coo to each other in chirps and growls. Human speech is so boring these days, inadequate for their needs; an animal's chilling hunger has split away the more human sides of their brains like their own teeth through flesh. 
Hunger for food, yes, but not just food. A still-beating heart pops between Raph's teeth as he chews, and through a haze of red he can still Leo leaning over another body, his lovely mouth stained black with blood and his eyes glinting pure silver in the moonlight. 
Leo feels that gaze and looks up at him, a smile dancing across his lips. It's the teasing, naughty little smile he's always reserved for Raph and Raph alone, and of all the recent changes in their lives that smile still makes Raph's breath catch. 
He wants and so, still chewing, he lets himself scrabble across the ground on four nimble limbs, too excited to bother with walking. He slams Leo to the ground, arms over his head, his brother squealing and wriggling playfully in his grip. 
Raph reaches into the nearest body, ripping out bands of stringy, torn muscle that can still be put to use. His hands blur over Leo's body, tying his brother's arms behind his back and binding his legs up tightly to his chest, laying him out as neatly as the rest of tonight's meal. 
He straddles Leo, the bodies of dead New Yorkers squishing under near them in a somewhat unstable, but suitable mattress. Leo looks like he's decked out in rubies and diamonds tonight, painted nice and pretty with the insides of unlucky fleshbags, and Raph's hot, aching cock drags against one of the corpses as he crawls near. 
Leo tries to keep his cute tail pressed into place, smirking like the little tease he is, but Raph simply leans down and sucks the tip into his damp, dripping mouth. Leo lets out a little squeak as he pulls his tail away, winking exposing his winking hole. 
Raph gives it a few quick spanks as a reminder not to hide next time, sending Leo writhing and churring in his restraints. Raph drinks the sound in, savoring like he did tonight's meal--like something he'd kill for, has killed for, and will undoubtedly kill for again. 
His hands are already nice and wet, so he just jams the first finger straight in. He could honestly fuck Leo now if he wanted to, after all the changes their bodies have endured, but he prefers a bit of finger-fucking instead, playing with his brother's tight little hole as Leo jumps and writhes like a marionette, tail thumping eagerly against dead flesh. 
Eventually, though, Raph gets impatient, and he surges without warning. Leo cries out at the sudden penetration, hugging Raph's cock with a desperation not unlike the humans who had clawed at unforgiving cement in an attempt to escape them. 
But Raph can be generous now, and he gives Leo exactly what he needs, thrusting with enough force to rip a human being apart from the inside out. Leo just sobs out a garbled plea for me as he pushes back, thighs shaking in an attempt to push wider. 
Raph leans down and kisses him, churring into each other's mouths as he fucks his brother hard enough to make dead bones break beneath them. Or at least Raph thinks that's what the distant cracking sound is; he doesn't really know, and he certainly doesn't care. 
All he wants, all he needs, all he is is Leo, Leo, Leo, Leo in his arms with a full belly and spread legs and pupils blown out with lust and love, Leo's lip breaking between his teeth so Raph tastes him to the dark and rotten core. Leo is his until the end of time, and unlike the poor souls in the alley around them--the poor hapless souls in the city, the world around them--that's exactly what they have.