ace, for one, can immediately tell that his little brother has a crush on you.
he was delighted to see his oaf of a younger brother (affectionately speaking, of course) managed to land a crew of respectable looking people. said crew managed to keep luffy on his toes and mostly well behaved, but ace saw that respect amongst the crew was mutual, there was a love there that only an idiot like luffy would be to find. he always had this god-like luck.
in fact, ace thinks luffy is especially lucky to have found someone like you. during his many years as a pirate, he's made it a habit of trying to analyse others and when his gaze fell on you and his brother he knew there was something...different there.
from what he could tell. you were incredibly patient. patient enough to allow his brother to cling to you like a baby monkey. luffy hadn't even hugged him after they'd reunited, yet you'd think it had been ages since he last saw you, the way he clung to you like you'd disappear.
"yn's super cool, huh, ace ?" luffy cheered, chin propped onto your shoulder and arm wrapped around it as well. you patted his arms, clearly embarrassed and trying to shrug his praise off.
luffy looked at you in confusion at your sudden silence. his face clearly way too close to you but still analysing your face like there was something to miss.
"what ? you are ! they're duper smart i'm tellin' ya ! knew i wanted ya in my crew the moment i saw ya !" he laughed, roughly slapping your shoulder.
by that point, ace knew something was up.
"the captain speaks too highly of me," you chuckled "i'm really not that great..!"
"luffy ! shut up !" you hissed.
"s'true ! you won't stop me from saying it ! ace thinks you're cool, too. right, ace ?!" luffy turned to his brother for support, but ace was sure that even his opinion wouldn't deter him. stubborn as a mule, that one.
he was sure he'd almost phased out of luffy's mind by now, his mission now solely to convince you of how cool you were while you tried to stay humble.
at some point ace even became referee in the matter of if you were as amazing as luffy said you were or not, luffy being uncharacteristically serious about it. so much so that you ended up having to grab his cheeks to shut him up. in the end, ace ended up having to mediate what ended up being a fight for your honour...between luffy and you. the person in question.
his brother was always a clingy boy, he'd climb on ace's shoulders, which usually led to wrestling. but he was more affectionate with his crew and especially to you.
he'd do everything and anything to get your attention, pulling silly stunts during dinner time that unsurprisingly ended with him getting a whack on the head from the cook for playing with his food. but he seemed unfazed when you laughed at his antics, smiling bright and wide like the spot on his head wasn't already starting to swell.
(he won't even mention the way he almost choked on his food when he saw luffy share a piece of his meal with you..)
luffy was always around to show you something cool, to tell you about something he saw or something his crewmate, ussop, told him. ussop would exclaim that luffy was a joke thief, but again, nothing mattered to his baby brother so long as you smiled at him, it seemed.
ace saw how luffy's eyes searched for you and your reactions first and foremost. he could tell he loved his crew dearly, the boy had his heart on his sleeve and couldn't lie to save his life, but ace could tell. he could always tell when it was about luffy, you were different.
and ace, for all his worries, is reassured he's found himself a group that will follow him with faith. and someone like you, who managed to captivate his brother so, and allow ace to see something interesting before he had to leave his brother again. though luckily, not on his own. at least as long as you were around.
before his departure, ace pressed a hand to your shoulder, leaning in close to whisper softly in your ear. "i leave my little brother to you. you take care of him, yeah ?"
he leaned back and chuckled at your flabbergasted expression. luffy was quick to lean in, pressing his hand to your opposite shoulder to demand to know what ace told you. "oi, ace !! what'd you do to yn ?!"
ace smirked, sticking his tongue out "not tellin' !" he jeered.
it's childish, something he'd do when both him and luffy were still kids. but which older brother doesn't enjoy messing with their younger sibling once in a while. and by the pout on luffy's face, he still had it.
"you take care of each other, kay ?" ace teased. luffy blinked, face melting into a blank expression before he raised a brow.
"huh ? course i do !" he grinned, looking at you again "right, yn ? i take good care of you, right !"
ace could only sigh affectionately while your groans and the captain's cheers faded from his ears as he made his way.
he could immediately tell that luffy had a crush on you. regrettably, even before the boy himself had. ace prays you'll remain patient and allow him to connect the dots on his own time.
but he thinks it probably won't take his dense little brother long to figure it out...hopefully.
