Blair's asked for this and he deserves it.
Jim's brings his hand down hard and hears the breath catch in Blair's throat and the pained, stifled grunt that follows. He leaves his hand pressed against hot, bright flesh and in a cool, steady voice continues the lecture.
Blair whispers his name, his voice thick with tears Jim doesn't want to see, and Jim's hand rises, falls, connects again. It hurts, but he can tell that he's pulling back; that slap had landed with far less force than the first few.
He hands Blair the paddle that lies on the bed, waiting. "Finish it," he says harshly, ignoring the tiny headshake, the bitten lip. Blair takes the paddle reluctantly, eyes guilt-sheened, cheeks flushed (Jim's ruining one of Blair's never openly admitted to kinks here, but he can't bring himself to care).
"Please, Jim --"
"Do it," Jim says softly, inexorable, merciless. "Six."
"Your ass is -- man, you really did a number on it already -- it's enough, Jim. Please, I said I was sorry --"
"Six," Jim says and settles face down on the bed again, his ass bare, jeans at half-mast, and waits for Blair to finish the punishment Jim's decided matches the offence.
Blair fucked up royally today, and they both know it. Blair hasn't tried to defend himself, which tells Jim plenty. Once, he might have accepted the sincere contrition, the promise to never do it again, I swear it, Jim! Months of being Blair's lover have taught him that the easy, facile apologies don't count for much once the first flush of shame have died down.
He would never strike Blair. He gets a sick lurch in his stomach when Blair gets beat up, bloody, bruised, shot -- hitting him, even a few token swats on Blair's ass, even if it left no more than a quickly fading redness, would be impossible.
But he doesn't need to spank Blair when he can punish himself.
Blair hates it, just as Jim would if the tables were turned. Hates seeing Jim in pain, hates that he's responsible for it -- and agrees to it every time, as Jim won't do it unless Blair does, because he needs to be chastised to feel absolved.
They both know that for all the faint purple bruises Jim will wear for a few days, Blair's the only one getting punished here.
And Jim's angry enough still to feel savage, brutal.
"Make 'em sting, Chief," he says, and doesn't hold back a cry of pain as the first stroke lands, even though it was a tap, tentative, shaky, and he'll make Blair do it again until he does it right.