"So, I hear you and my little brother are pretty close..."
There's a faint scraping of steel as Zoro's thumb pops Wado loose from its sheath, and Ace laughs out loud at the swordsman's dread-filled expression. "Chill out, man! I'm not gonna give you a hard time."
Crouched on the railing, he looks disturbingly like a slightly more mature version of Luffy, except for the freckles. Behind them, Zoro can hear the other Straw Hats arguing excitedly with the captain, demanding to know exactly how he and Ace can possibly be related. Luffy is laughing, and Zoro glances back to see if anyone's noticed this side conversation.
"Anyway," the division commander continues, tapping the swordsman's shoulder to get his attention again. "Once Luffy decides he's going after something, there's no arguing with him."
"So I've noticed," Zoro mutters dryly.
"And he's got a tendency to really leave his mark on people he meets." Ace raises an eyebrow and grins widely when the other man flushes darkly. "Yeah, you're not doing such a great job of hiding that."
Fuming with mortification, Zoro silently vows that he's going to tie Luffy to the anchor once his older brother leaves, because he's getting tired of telling his captain to quit leaving love bites in obvious places. He's already been catching hell from Sanji and Usopp all morning and stubbornly turning down Nami's snide offers to lend him her concealer, and now this.
"Just do me a favor-"
The swordsman tenses, because surely here come the accusations and thinly-veiled threats that imply he's not good enough for Ace's little brother and how he's going to be skinned alive if he breaks Luffy's hea-
"Make sure he's happy and keep an eye on him for me, huh? My damn kid brother's always getting himself into trouble, y'know?"
"Ah," Zoro blinks, surprised that he's not getting the lecture he expected. "Yeah, I can do that."
"Thanks," Ace grins hugely, clapping him on the shoulder. "Lemme borrow him again real quick and then I'll be on my way... Oi, Luffy! C'mere a second."
Recognizing that he's been dismissed, the swordsman stands aside as the brothers exchange a few final words, and when Ace asks the crew to take care of Luffy, he knows the flame-user's staring straight at him and offers back the briefest of nods.
xxx
Some time much later, when the somber-faced Perona presents him with a newspaper depicting his grieving captain, head bowed in prayer, at the Marineford ruins, Zoro will curse himself bitterly, knowing that he'll be forever haunted by that short conversation.
That evening he will swallow his pride and approach Mihawk with his unlikely request, determined to somehow make amends for his failure to keep his promise to a dead man.