No matter how many battles they fight, they never end their war.
Even when they're "co-operating", they still take every opportunity to duke it out, destroying the plans of the both the Shinsengumi and the Yorozuya with their violent bickering.
Their faces screwed up in anger, fists and sometimes sword flying, screaming the most hurtful insults they can think of in the heat of the moment, they've fallen into a pattern.
Kagura grits her teeth, throws punches that could level houses, and then faces an irritating blank expression, or worse, a smile, from that sadist, again and again.
Okita dodges the brutal attacks, the irrational, childish rage, and then cuts back with his words and his own attacks as best he can; he's much better at hurting people than she'll ever be, but then again, she's stronger than his weak human muscles will let him become.
She hates his fake little smile and sadistic little jokes, feels an edge of irritation at a face and strength that remind her of the cruel brother who left. Deeper than that, everything he does makes her feel something stirring her blood. He calls out the Yato in her, makes her itch for red battlefields and glorious, screaming victories, feel the primal rage that's causing the death of her clan.
He's a cruel, sick little boy who, she feels, has no respect for delicate maidens. He's a terrible policeman and a worse ally; the only way she's sure he won't stab her in the back is being behind him holding a bloody knife.
But… He can keep up with that Yato inside her, and leave the battlefield essentially unchanged. His body might as well be made of matchsticks and newspaper, fighting her strength, but... Even after she attacks his body, counters his strength, breaks his leg, he's still there, still sadistic, still challenging her.
She hates him, sure; but it's a hate that feels a bit like friendship. When she met a that silver soul and giant dog who she knew could take her on and remain unbroken, she'd sworn that she'd love, follow and protect them as she could. That kind of mindset didn't set her up well for rivalry. But she still, deep in her bones, needed a nemesis, someone to hate honestly, someone to get back up and keep fighting her. That sadist is nothing, for her, if not hateful and unbreakable.
She can't beat him, and it's wonderful.
Sougo, meanwhile, knows he started this cycle, with his barbed words and competitiveness. But she's fuelled it too. He's got plenty of rivals to throw down with if he feels the need, and her petty grudge matches tend to happen at the most inconvenient times. She's a petulant, irritating child who thinks she can play with the adults just because she's strong, and every time he sees her he's reminded that he's one, too.
This little China-girl is just some minor irritant, a fly to swat away before he hunts Katsura and murde-supports his commanding officer. If he wanted to, really wanted to, he could slip past her loose defences and unskilled hits in a second and cut her into ribbons.
Yet Sougo knows he never will. He has a code of his own regarding civilians and women and people other than Hijikata that Kondo hammered into his sadist's soul. Not to mention that he'd be making Sakata Gintoki and a good part of Edo his enemy.
More than anything, however, he doesn't feel right going full strength against an enemy that's not doing the same to him.
Always, even when she's in full berserk mode against him, he can feel it; she's not fighting to kill, or even really to hurt. She laughs and acts triumphant every time one of her monstrous attacks actually connects, but he can see an apology to him clawing at her throat and an admonition against herself weighing down her back.
He can sense that there's a part of her that would be happy to see him covered in blood, that wants the win, the control, as bad as he does, but she beats it down. She fights him with a strength that would break a normal person but, Sogo knows, is enough to sting him for a while, but rarely really injures.
She makes him remember the tears on his sister's face when she found the animal bodies in the woods, the quiet disappointment from Kondo when he'd gone too far, the moments when he'd actually been glad that Hijikata had been there to stop his sword.
But she'd taken that irresistible need for control and victory and made it a joke, a nothing; made herself a silly girl who caused property damage instead of a demon covered in blood.
Sogo watched her, and fought her, and never really got serious, because she had hands stronger than his, but her eyes were always as gentle as his sisters'.
She's always beating him, even when he wins.