Luffy has this big X on the centre of his chest, gaping and thick and gnarled skin and pale bumps and thick skin.

Zoro hates it.

Usually, he's proud of scars. They're something to be proud of, he thinks, some reminder of a glorious battle or of something that helped teach him to grow, he can't condemn Luffy because he had countless thousands littering his own torso and he shows them off with pride, a small, smug smile lifting at the corners of his features when he sees them.

And usually, with Luffy, it's okay, it's just the reminder of a battle they had, a reminder of a time they got stronger, got better, and he is proud.

But this scar is different.

This scar isn't about glory or a battle or any of that, this scar is about the time that Zoro failed, the time that he wasn't there for his captain, and he hates it with a passion.

What's even worse is that Luffy never covers it up, so he constantly sees it, a reminder of his failures and shortcomings, of the time that he couldn't protect his captain because he was weak and useless, of a time that he was overconfident and stupid.

He finds Luffy rubbing his knuckles against it one day, expression pensive and eyes trained on his hand, and Zoro grabs Luffy's hand. "We're training," he says, no explanation, none needed.

"Thanks," Luffy says, smiling softly, for once not chattering like a monkey about something weird that he found or saw.

Zoro hates it. He hates it so, so much.

Why don't you cover it up, he wants to say.

Why do you keep it there, he wants to ask.

Why, why, why, he knows he can't, though, because he understands perfectly, that Luffy doesn't want to forget, that he can't forget, because all these years later Zoro still blames himself for Kuina falling down the stairs, still keeps his swords at his sides and tries to make sure everyone's inside when it rains.

(And he knows it's odd, knows it strange, but nobody prods or challenges it and they all have their odd little quirks so Zoro knows that he can't questions theirs as they don't question his, an unspoken promise hanging in the air.)

Someone that they fight, some stupid person that they're fighting, laughs at Zoro and asks, want a scar like your captain's and Zoro's face burns, but he can't fight because Luffy holds up a hand and laughs, "I'll handle this guy," cracks his neck to the side, punches the palm of his hands, eyes cold as ice as he snarls, "Don't threaten my first mate," and when he's done Zoro just sighs.

"I could have handled it," he says, and Luffy laughs, linking his hands behind his head and puffing up his chest as tosses his head to the side.

"I know," Luffy laughs, the unspoken, but you're mine hanging in the air.

Something twinges in Zoro's chest, proud and full and happy, "Stupid," he says, and Luffy just holds his hand, still laughing.

There's something about the X on Luffy's chest, proud and full and on display that makes Zoro think, this is my captain.

He hates it. He wishes it weren't there. He hates going to see his captain and always seeing that stupid, stupid X on his chest.

But it's part of his captain, and Zoro knows that if it weren't for the X in Luffy's chest, it would be something far worse.

He imagines the images of Ace they put in the papers, mouth open, a gaping hole in his chest, flesh burned so badly that no blood could come from the cauterized wound. He imagines Luffy like that, eyes wide, torso gone, and knows that Zoro would regret it for the rest of his life, being too weak to protect his captain.

And maybe it's selfish (he knows it's selfish, he is so, so selfish), but he's grateful for Ace's death. Because he knows that if it weren't for Ace's death, it would be Luffy's in his place, and yes, Ace was great, and yes, he knows that Ace's death made Luffy sad but Zoro just wants his captain alive, and he is willing to let the rest of the world burn if their crew can stay safe and Luffy can keep smiling.

Luffy has this big X on the centre of his chest, gaping and thick and gnarled skin and pale bumps and thick skin.

Zoro hates it, and he'll never allow Luffy to get a scar on his chest ever again.