James never does love anyone quite like he loves Sirius, not even Lily, because he lives for Sirius.
He lives for Sirius’ grin, crooked and bleeding red and cracked with something not quite right, when he breaks Mulciber’s jaw for fucking with Mary MacDonald, for the way he keeps going even after Mulciber’s face is a mess of blood and bone and broken teeth, and smiles right at McGonagall afterwards, smooth and charming and everything people expect him to be.
The next morning, Mulciber’s glaring from the Slytherin table, and Sirius just grins, all pretty white teeth, a promise as much as any with blood still crusted on his knuckles.
(It doesn’t shock James, years later, when they so readily accept him as a mass-murderer, a Death Eater, a coward.)
He lives for the cigarette held loosely between Sirius’ lips as he sits back, smiles up at Death Eaters and Ministry officials and ICU members without a care, except that’s wrong because he cares, he cares so fucking much, that’s why he cuts off the arm of the man who goes to cast the Cruciatus Curse on Marlene McKinnon when they’re sixteen and going crazy in that castle, or why he stabs a girl in the throat when she tries to call for Death Eaters from in the kitchens where they’d herded all the kids after spellfire cut through Hogwarts like fireworks.
(Why don’t they understand? Why can't they get that?)
He lives for the way Sirius duels like he’s dancing, fast and sharp and far more dangerous than any Death Eater, how he splits men and women down the middle with quick flicks of his wand, how he holds their heads in his hands and stares them straight in the eyes and just pulls, runs his fingers through the folds of their minds even as they scream because he doesn’t bother with finesse, doesn't bother being nice with it, because what is nice in this war of theirs?
He finds names, though, names and faces and all their little meet-ups, then pulls himself out of their memories, cocks his head to the side as he listens to them gurgle on spit and blood and the broken frays of their minds. He doesn’t kill them, because what’s the point? He leaves that to the rest of the Order, because his Death Eaters are no use to him after he’s dipped in everything that they have, everything that they are, torn apart their minds and refused to sew them back together.
(James wonders, afterwards, if Peter had stopped looking Sirius in the eye because of this, because Sirius wouldn’t hesitate if he thought something was wrong.)
(James thinks if he would have let Sirius do that, do it to one of their best friends.)
(James knows he would have.)
He lives for the way Sirius leaves, disappears, for six days when he finds out his baby brother’s dead, as he realizes that they are children and fighting a war and that they’re all going to die, and that Sirius would be damned if he let anyone hurt him or his, so he goes after them, cripples their magic and tears at their minds and just twists that little bit, just enough for it to hurt.
But then Sirius cradles baby Harry so very carefully when Lily’s in bed and James is beaming and Sirius has still got blood on his collar from that morning, his hands bruised and shaking, and he’s been away for months now in a mess of red and black and green. And James just knows that Sirius will love Harry, will love him entirely, and that he’ll look after him, just like he looks after James and Remus and Peter, Lily and Marlene and Dorcas.
(Anyone that’s his, because that’s what they are, what they always will be, and he will bare bloodied teeth to anyone who tries to get between them.)
But then James sees Him come into his home, yells for Lily to run with Harry because nothing can happen to his baby boy. He tries to fight like Sirius - Sirius, who would have brought the entire house down before letting anyone near Harry; Sirius, who would smile prettily and snap bones out of place; Sirius, who would look every bit a Black as he gutted Voldemort with a kitchen knife - but he can’t, because he’s not Sirius, and he falls in a flash of green so fast that he doesn’t even really feel it, not beyond the jolt of terror for his boy, for what Sirius will do because James is his and James doesn't have permission to die.
(But James is dead and it all happens so quickly that he can’t do anything about it.)
He follows Sirius for years afterwards, sneers at once-friends who are happy to lock him up for years, to laugh as Dementors eat away at his memories, and thinks it’s a cruel, special, kind of punishment for a man who helped win their war.
But then Harry, his little Harry, is in the Minister's paper and Peter’s there too and Sirius gets himself out of Azkaban that night, pushes shards of stone into an Auror’s eyes and takes the wand, casts a spell at Dementors that make them shudder because Sirius has never been able to cast a Patronus so he’d found other ways, better ways, ways that make them choke on glass and bleed death, and James can’t find it in himself to be sorry, because this is what Peter will be getting and this is why he hid, ran as far from Sirius as he could get as a fucking rat, because Sirius won’t stop, not after this.
Except he does.
He lets Harry stand between him and the traitor, lets Peter run, lets Harry think he’s saved Sirius from murder when James knows Sirius would have done much worse if he got his hands on Peter, would have cut away at everything he had left until he was a shell, rotting around his bones.
(James almost wants to see it, wants to see the man that put Harry in Voldemort's hands scream and beg and suffer, and Sirius will do it without thought because what's another one to his list?)
Equally, Sirius lets Harry think that he’s good, even if he doesn’t really hide what he is, because all Harry knows is his Godfather was imprisoned for something he didn’t do and that makes him innocent. Harry doesn’t know that Sirius’ hands are painted, drowning, in red.
McGonagall does, though, and so does Dumbledore.
They’d seen Sirius spit blood at students when they couldn’t get back up after he’d beaten them down, sometimes with a loose tooth or bits of his tongue too, and they hadn’t stopped to think that Sirius would never give James or Lily or Harry up, would cut off his wand arm before he let them get hurt.
And Harry must, should, realise something is wrong there, when Dumbledore traps Sirius inside Grimmauld Place and McGonagall says to him absently, “There’s nothing of the boy I remember,” when really Sirius is better, because this way he’s not splitting people’s skulls or shriveling up their organs.
(James isn’t sure which he prefers, because this Sirius is rotting in his father’s chair with a bottle of Firewhiskey in one hand, a cigarette in the other, anything to stop the scratching at his skin, the urge to rip and maim and kill that's set bone-deep and deeper still.)
But then Sirius dies. He isn’t laughing, because Bellatrix catches his back when he steps to take the spell for Harry, and James thinks this is right, this is how Sirius dies - not in his cell in Azkaban, and certainly not in Grimmauld Place, but protecting Harry, protecting his.
And James gets to meet Sirius again, holds the ragged and gaunt man as he stumbles through a gateway and into James’ arms. Sirius - too cold, too thin, too bruised - shudders, sobs into James’ shoulder, touches him with trembling hands and says his name with a new kind of reverence.
James wouldn’t believe that this man is his Sirius (young, handsome Sirius, who grinned as if to say, "Is that all?") if he hadn’t watched it happen, hadn’t watched Sirius crumble and rot away, but he is and he’s apologizing and James still can’t get a word in, so he just holds him tight, hates the feel of too-sharp bones and papery skin, but at least it’s something, at least it’s not nothing, not anymore.