Sanji's been in plenty of bar fights since signing on as a Straw Hat; protecting young girls from drunken sailors, incurring the wrath of men whose wives flirted back with him coyly, cleaning up after a certain rubber brat and swordsman duo picked a fight with a rowdy crowd. He's only gotten stronger in his time at sea, and a scuffle at a pub isn't close to noteworthy in face of everything else he's seen and done.
But this time is a little different.
This time he leaves the bar with a split lip and Luffy in tow, so angry he can't even see straight. His grip on Luffy's wrist might have broken it if it wasn't rubber, and Luffy stumbles once or twice trying to keep up.
"Hey, Sanji, slow down."
"What are you in such a hurry for?"
"If I slow down I might go back and actually kill that guy. Do you want me to kill that guy?"
He's true to his word, doesn't slow down even to glance back at his captain's expression so he has no idea what Luffy's face looks like when he says, "How come?"
"No, you're acting weird." Luffy tugs at his arm experimentally and then yanks it away when Sanji still doesn't let go; falling back a few steps and glaring when Sanji turns around. He's rotating his wrist like he doesn't realize he's doing it, and on any other night Sanji would have felt shitty about that; as it is, the anger falls away and leaves him feeling exhausted. "What's wrong?"
Luffy really doesn't understand. But that's the whole point.
"You have no sense of danger," Sanji tells him quietly. "That guy was bad news."
Luffy tilts his head and blinks at him, uncomprehending. "But he bought me a drink. That was pretty nice of him."
"He had ulterior motives, captain."
Sanji shakes his head, knowing a hopeless case when he sees it, and holds his hand out again. "Never mind. I'm sorry about dragging you."
He lives with Luffy, spends every day with him, cooks his meals, dives into roaring ocean waters when he's drowning, throws a blanket back over him when he kicks it off at night. He knows the ins and outs of the boy who trots over to take his hand, he knows exactly how irritating and wonderful he is, exactly how much of a prize he would be to take home, even without the bounty on his head.
Sanji also knows how Luffy must look to an outsider; Sanji himself was an outsider once, years ago. And to people who don't know him, who haven't seen the miracles he can produce with nothing but two fists and a stubborn ferocity, his captain is small for his age and his rank, thin, with a mess of dark hair and round brown eyes, looking out of place in any dim seaside bar, with his straw hat and bright red shirt. Son of the barkeep, maybe, or just a kid waiting for an older brother.
And Sanji, who's been in plenty of bar fights since signing on as a Straw Hat, knows a particular type of danger when he sees it.
So when a man took the stool next to Luffy's and ordered him a drink, Sanji let it be; there was a beautiful lady sitting next to him, after all, and she was halfway through describing the culinary school she once attended in her hometown. It was actually very interesting, and she was throwing out cooking vernacular that made Sanji swoon, but a born chef is also a born multi-tasker; and when Luffy's company dropped a pill in Luffy's cup, Sanji saw it from his seat three tables down. He stood up so fast his chair fell over, startling the poor girl from her story, and didn't even stop to apologize on his way over to the bar. He leaned over Luffy to lift the glass away from him with a short, "Excuse me, captain," and without prelude, smashed it into the stranger's face.
So what if the stranger had friends? So what if they managed to get a hit in while Sanji was busy pummeling the bastard into the ground? They were looking at Black Leg of the Straw Hat Pirates, even if they didn't realize it, and their sorry excuse for a mate had tried to drug Luffy.
And when the bartender fired a rifle round through the roof and kicked them out, Sanji grabbed Luffy's arm, stepped over a broken table, and left shattered ribs and collarbones in his wake.
And looking at Luffy now, as he swings their joined arms back and forth, Sanji has half a mind to go back there and finish the job for real.
"So you were looking out for me, then," the rubber boy says, since that's really the only part of the situation he's managed to get a grasp on. His cook nods once and is rewarded with a wide smile. "In that case, thanks Sanji! Sorry I don't know what ulterior is, but as long as you do, then I don't have anything to worry about."
And if it was anyone else, Sanji would have grabbed them by the shoulders and shaken them hard, demanded they get a grip and see the world for what it really was, open their eyes to the danger they had been in moments ago.
But it's Luffy, who's already seen the absolute worst of people, the absolute worst of the world, the dark and the gritty and the desperate. And if Luffy can come out of suffering and war and heartbreak and still smile like he's never known hurt, and laugh at Usopp's tall tales, and trust some stranger in a dark bar, then it won't be Sanji who ruins it for him.
Instead he'll smash in faces and break knees, get banned from restaurants and hotels, look like a thug in front of all the women who see it; and he'll do all of it so Luffy can smile at him, just like he is now, and have one less bad memory to take with him when they go.
"Yeah," Sanji tells him, tightening his grip on Luffy's hand but not hard enough to hurt him this time, "when it comes to stuff like this, I'll take care of it."