[ETA: I updated the title to align with my vision.]

They don't usually spar. Cass is better than Jason and they both know it, so there is no sport in it for her. Besides, Jason never relents, only stops when Cass calls it quits once he's on the verge of injury. And she only does so because the only thing worse than dealing with a pouting Bruce is a benched Jason.

So, no, they don't spar, but they still compete. Over silly things like who's the first to finish folding the laundry or who can take the most groceries inside on one trip. Over stupid things like how many batarangs can they sneak out of Batman's belt before he notices, or who falls the furthest before activating a grapnel. Over bruising things like who rescues the other most or who gets lectured first.

So often, too often, it's a tie, and Bruce's lips press into a firm line that holds back a litany of "I expected more"s and "you're too old"s. The crease in his brow gives away his confusion at not being able to use the classic "you should be setting an example" because, due to cosmic irony, Jason and Cass are twins.

Sort of. Lady Shiva's almost son and forsaken daughter. The daughter Bruce always wanted and the son he can never have. It's kismet. A taijitu – bright, unyielding strength meeting covert, unbreakable will. They should work together better than this, but something broke between them long before Cass had ever met him, and she can't fix it alone, doesn't know that she wants to.

So they compete – for crime scene trophies, for their siblings' laughter, for Bruce's smiles, for each other's respect.