"Hey Luffy, how'd you get that scar on your face anyway?"
The question comes from nowhere, but Sanji's curious, and they've got nothing else to talk about; they're watching the ship while the others go to town for supplies, and the clouds are moving particularly slow today.
Luffy blinks at him upside down and touches the pencil-mark scar under his eye. "Oh, this? Heh, that happened a long time ago!" He grins wide, looking up and away. "I was trying to prove to Shanks I was brave enough to be a pirate, so I stabbed myself in the face."
It takes Sanji a moment to digest that, then another to form a witty repartee; "What?"
"Well I was only six, it was the only thing I could think of."
"You were six when you stabbed yourself in the face."
Luffy giggles at him like he's finally in on a hilarious joke, but Sanji isn't laughing. As a child learning to maneuver in a professional kitchen, he knicked his fingers quite often; but to lift one of those dangerous instruments up, and to plunge it into his own skin with certain intent, just to prove a point-
"You're a real idiot, you know that?" he bites out quietly, and Luffy tilts his head like he honestly has absolutely no idea where Sanji's coming from. The cook takes an aggressive drag from his cigarette, cutting his eyes away to glare a hole in the deck. "I can't believe you."
Luffy hums, thoughtful. "I guess it was pretty dumb."
"You guess- "
"If Ace was my brother back then, I bet he would've beat me up for something like that!"
Sanji glances at his captain, and feels the ire float away like a plume of smoke. Doesn't speak for a long moment. Has no idea what to say to the boy who rolls onto his back and holds his hands up against the sky like it's a blue he can feel.
They don't talk about Ace; they don't talk about him, or the war, or the long months that followed it, because they don't know if it would hurt him, and they're just not willing to take the chance. If that means living with a starving curiousity, so be it.
But... he started it.
"He wasn't your brother when you were six?"
"Nope! I met him after I met Shanks. We have different parents. Sabo too!"
Sanji reaches out to card a hand through Luffy's hair, because he's close, and because he can, and because he should have two years ago. "Sabo?"
"My other big brother. He died when we were still little. He was so nice to me, even though he was unhappy."
The chef closes his eyes and rides out the swell of anguish. By the time Luffy rolls over onto his stomach, propped up on his elbows with his hat somewhere by Sanji's knee, Sanji's face is arranged back to its default setting, and he meets his captain's gaze unflinchingly, but Luffy can see straight through him.
Luffy can see straight through all of them.
There's a whole world of promises Sanji wants to make him; selfish promises, childish promises, to make himself feel better, to make Luffy smile right here and now, but instead he tilts his head back against the rail and smokes, because he could never be so cruel.
Luffy remembers promises, and as long as there's a chance they could all die tomorrow, there's a chance any promise Sanji makes could break and die cold, and Luffy would always remember, and Sanji just can't.
He glances down at his captain again, and Luffy squints his eye shut when Sanji rubs his thumb over that scar; achingly familiar, a part of Luffy as much as his hat was, always coupled with a stretching smile.
"You could have died when you were six years old," Sanji says, almost to himself. "And I wouldn't be sitting here in the grass with you, waiting for the others to come home for dinner."
The rubber boy sits up, blinking. "No, you'd be somewhere else, doing something else. Huh, that's a funny thing to think about. Would you be a famous cook?"
I'd still be just a nobody in East Blue if you never showed up and gave me the courage I needed to leave it.
"I'd rather be an infamous pirate."
He says it because he knows Luffy will laugh and agree, and that laughter is enough to make the tight coil of unease in his chest loosen at the thought of a world without the Straw Hat Pirates, a world without the flag that's come to symbolize to him everything worth dying for, a world without that scar and that smile.
Luffy's attention is slipping away as they hear familiar, dear voices on the gangplank- Zoro and Usopp both promised to bring him back souvenirs, and once everyone's settled it'll be time to eat- so Sanji reaches over for his hat and jams it on his head.
"I bet you've learned a lot since you were six."
Tilting the brim out of his eyes, Luffy smiles.
Sanji can't make him any long-standing promise, because there's always too much at stake. But he can make him smile, and make him dinner, and make him swear off hurting himself like that ever again ("I mean it, Luffy, if I ever catch you with a knife in your hand- " "I was six!") and when the time comes, if it comes, Sanji can make him proud.