Author's notes: In which I blur the boundaries of the concept of nakama and then gleefully run around. My thesis defense is tomorrow. This is what happens when I get too stressed and have Marineford on my mind.
No member of the Straw Hats denied that there was a certain gravity about their captain. They felt drawn to their captain in a way that they felt drawn to no other member of the crew, no matter how dear. They never called that gravity by name, because they never mentioned it aloud. But every single member of the crew knew what it was, accepted it and gave in to it as inevitability.
Robin had felt hints of it every now and again, but it had really struck her at Enies Lobby. When, despite everything that she was, her captain had so calmly told her that she was to come back to him whether she wanted to or not, and that if she still wanted to die then, so be it—when he had coaxed out of her the long-suppressed will to live—when he had lain there in the tower after defeating Rob Lucci and told her that they were going home—she had known it then without a doubt. She had known that no matter what happened in the future, no matter how many years and decades went by, no man or woman would ever hold her whole heart in the palm of a hand like Luffy did. During the two years that they were apart, everything that she did, she did thinking of Luffy.
Chopper had felt it the moment that Luffy had called him his comrade. Chopper had spent so many years being used to solitude that it hadn't really struck him how lonely he'd been with no one to talk to but Doctorine until that moment—and so the joy of it had been multiplied exponentially. But the identification of the feeling had taken him longer. Only as he sailed with all the rest of them did he realize how much stronger his attachment to Luffy was than to all the others. Because Luffy was a monster too. Because Luffy had been the one to want him in his crew for being him not because he was a doctor or (supposedly) edible, or even cute. He hadn't known that it was possible to feel something stronger than what he'd felt for Dr. Hiruruk or Doctorine until Luffy. Through the two years, every new discovery he made was another treasure he couldn't wait to share with Luffy.
Brook had felt something similar for his former captain, so it didn't particularly surprise him when he felt it come over him after everything at Thriller Bark was finished and Luffy told him about Laboon and asked him to join his crew one more time. He didn't know when the realization struck him that his feelings for Luffy were so much deeper than they had been for any one member of the Rumbar Pirates. But if he hadn't figured it out before, it certainly would have struck him when Franky had remarked with admiration that it was good of him to abandon stardom to rejoin them—because such an idea had simply never occurred to him. Life as a star had been heaven for Brook, and he knew there had been a time when he would have fantasized about remaining a star—but with every song he had sung the past two years, he thought only of returning to Luffy.
The rush he had felt when Luffy told him to get onto the Going Merry because they were already comrades had so alarmed and overjoyed Usopp that he had shouted perhaps a little more than he should have. Because he knew that rush: he had felt it the first time he'd seen Kaya laugh. He had spent months trying to convince himself that it wasn't what it seemed to be—and later, he would blame his denial for the decision to fight with his captain over a decision already made. Because he had inadvertently accepted it as he begged for forgiveness there amongst the rubble, shouting across the expanse of water between the Sunny and himself. All through the years that he trained with Heracles, he swore never to be a vulnerability to Luffy again.
Sanji had felt it during the battle with Krieg, growing and expanding as Luffy determinedly defied every preconception Sanji had about the way the world was supposed to work—and then won anyway. He had convinced himself at the time that it would be something he would eventually feel for all his crew mates (except maybe the moss head). But as time went by, what he felt for Luffy grew deeper faster than what he felt for any of the others. All traces of potential denial were further blown away by his period of "maidenhood" at Kamabakka: he had indulged in many a fantasy about being swept away by his prince charming, but not one of those fantasies had featured any "prince" but Luffy. Though frustrating, it was also the only reason he could live with knowing that Robin-chan and Nami-san felt the same. And when he remembered the elation of seeing Luffy again after two years, he found himself thinking that maybe it wasn't so bad after all.
Franky had taken the longest to figure it out. He had admired all of the Straw Hats, certainly, and he had known that his admiration for the captain who did the impossible without even hesitating for a single member of his crew was several notches higher than for the others. But he had believed his emotional attachments to be only towards the Sunny and Nico Robin at the time. It took the two years of separation for him to realize that the attachment to the Straw Hat captain that he had observed in the others was something that he shared after all. When he installed the hair control switch, he thought of how excited Luffy would be to see it. With every change he made thereafter, he thought of Luffy, and knew that this feeling had been there from the very beginning—he simply hadn't noticed.
Emotion wasn't usually something Nami had to deal with during a heist, because after all, her victims were mere pirates. Then Luffy came and turned her world upside down. She had noticed the emotion in Zoro, and shrugged it off as part of the pair's eccentricity. But something about their determination, about Zoro's loyalty, about Luffy's sense of righteousness, caught her up and she decided it wouldn't be so bad to join them for a little while after all. It crept up on her before she had a chance to stop it, and by the time she realized it, it was too late. She resolved to enjoy it while it lasted, braced for the inevitable betrayal that would turn everything back around—bracing herself to lose this piece of her heart and be alone again. But Luffy came to get her, and refused to listen or leave. And then when she'd finally broken and everything came tumbling down, he was right there, putting his precious hat on her head and declaring that of course he would save her from the nightmare that was her life—and he had. Nami knew then and there that she was ruined for any other man. Her world had narrowed down to Luffy, and no matter how idiotic he was or how he irritated her, Luffy was her world whether together or apart.
Zoro couldn't have said when he had fallen, or even when he had realized he'd fallen, even if he had wanted to. All he knew was that in a marine base tied to a pole and starving and thirsty, he had pledged his loyalty to a rubber boy who said he would be pirate king. He had suspected then that he might lose his heart to the boy. He hadn't realized that in the blink of an eye, he would find that he'd lost his dreams, his soul and his pride to the boy as well. But by the time that he realized the were gone, it seemed so ordinary that he couldn't bring himself to mind. More than he wanted to be the greatest swordsman, he wanted to be the swordsman of the pirate king. Luffy's dreams was suddenly more important than all the dreams and promises Zoro had ever made, and so he bowed his head to his rival and became his pupil. Roronoa Zoro, the man who would submit to no one, found that there could be no greater position in the world than that as the right hand of Monkey D. Luffy.
And if Luffy never knew the depth of his comrades' affection for him, not one of them minded. He was their captain, and now that they were his crew, nothing would ever happen to them.