What they're doing is dangerous. It’s so dangerous, even if they’re both trained ninja, even if Raph’s fingers tighten and relax ever so slightly in time with his pistoning hips, giving Leo the occasional shallow breath. His eyes are clearer than they’ve been in a while and his hands are steady, but that doesn’t matter, because he could still do incredible damage without even meaning to. 
Leo knows this; of course Leo knows this, Leo’s voice hasn’t been the same since Oroku Saki choked it into a new shape. But the weight of cold claws around his neck is one thing and the warm, callused pressure of Raph’s is quite another. 
He’s out on the edge of everything and he loves it, same way he loves launching himself off a roof or charging through a crowd of enemies, swords flashing. He’s shaking all over as he balances on Raph’s lips, lifting himself up and down as best as he could, but it’s not fear that makes him tremble, just the white-hot heat of excitement searing through his neurons and dragging him towards his second orgasm of the night. 
Leo’s supposed to be above such things; he’s the same one, the cool waters to Raph’s anger. But Raph knows that’s bullshit, knows what he really is, and it’s the all-seeing weight of his dancing green eyes that turns Leo on the most. 
Being seen like this in all his strange, wanting glory is a privilege, one he savors, same way Raph savors how Leo knows that he gets hard half-strangling people and doesn’t think he’s a freak. It’s a special feeling, a level of trust rare even in their close-knit family, and they’ll both risk a lot to feel it a little longer. 
Raph groans, pace picking up, and Leo tilts his head back. Through blurry eyes he can see stars whirling around them and he’s got a vision of himself hurtling through space like Captain Ryan, or instead of a captain’s chair he’s sitting on his brother’s dick. 
The thought makes him giggle, or a choked squeak that could be a giggle, and something about the sound makes Raph growl. He grabs Leo by the swinging mask tails and yanks him forward, pressing their lips hard enough to sting. Leo flails, raking his shaking fingers down his brother’s shell. 
Raph pushes harder, stealing the last of his air, and Leo shudders all over, cock weeping freely. He thinks he might pass out or come, whatever’s first, but Raph sends him swinging backward instead, loosening the grip just enough for Leo to let out a strangled gasp. 
He’s quick about gathering fresh air, taking care not to hyperventilate, because Raph is still fucking him hard with no signs of stopping and soon he’s going to drag Leo back over the edge, back into that blurry, smothering half-world they’ve discovered together. And Leo will let him, because he knows, in a place deeper than logic or good sense, that however close they come, Raph isn’t going to let him die tonight.