(A/N: I wonder if maybe Luffy's body works anything like Wally West's? Probably not, but maybe sort of.)
"I don't understand," Nami said quietly, eyes trained without blinking on her captain's face. "What's wrong with him, Chopper?"
The rubber boy blinked once, heavily, and smiled long and slow. "I'm okay," he insisted, for what felt like the hundredth time, and Nami looked like she wanted to hit him.
"You can't stay awake," she snapped, concern lending her voice a blade. "You fell asleep on the rail today and almost drowned, Luffy! That's not okay!"
He frowned now, rubbing his eye with the heel of one hand, and protested, "It was an accident. I told you that already."
She opened her mouth, but Chopper leaned between them with a hoof out to captain and cartographer both. He directed his stern look toward the latter, because he didn't have the heart to scold Luffy, who was pale and swaying where he sat. "Nami, if you're going to upset him then you can't be in here. Send Zoro back in please."
A lesser man might have quailed under her scowl, but Chopper was their doctor and those were his orders, so he didn't let eyes loosen even a little. And sure enough, her face softened and she rubbed a hand over her forehead.
"Of course," Nami said gently. "You're right, Chopper, I'm sorry." She leaned forward without hesitating to kiss Luffy's hair, and let her eyes linger for just a moment on his thin shoulders and the tired curve of his spine, before standing back and moving across the room. "I'll send your first mate in for you, alright, captain?"
Luffy's smile was a little slow, but Nami was patient; and when he said, "Alright, Nami," she smiled back and closed the door behind her.
Chopper watched the smile sort of unhinge from Luffy's face and fall. The reindeer frowned unhappily. "Luffy, why won't you tell me what's wrong? I know you know. I know you do."
The scarred boy shrugged, his eyes only half open and glassy. "I'm just tired, Chopper. I'm okay."
The door opened, and Zoro stepped in. His swords were still where he left them, by the chair at Luffy's bedside, and Luffy smiled widely when he sat down.
"Hi, Zoro," he said, and Zoro didn't smile back but the green in his eye was soft like spring grass. He reached out and pushed Luffy back down against the pillows with one large hand against his chest.
"Go to sleep."
Chopper watched with an anxious twist in his stomach when their energetic, excitable captain did exactly that.
"I don't understand," the young doctor murmured. "He doesn't have a fever, he doesn't have any symptoms that I recognize, he's just so tired."
Zoro didn't reply for a long moment, but Zoro knew their captain best. Chopper knew, watching Zoro watch Luffy, that he knew of something, or would think of something, and sure enough;
"Maybe it's the meals," he said suddenly, the way someone does who's had the same thing on their mind for awhile; and Chopper tilted his head at him.
"We're rationing our meals lately, aren't we? Because the aquarium is empty, and that stupid Fish Man we fought last week drove all the fish away for miles." Zoro's eye was steely when he cut a glance Chopper's way, and the reindeer was absurdly relieved when he turned it back to Luffy again. "Until the winds pick up, we have to make due with what we have. That means one, two meals a day. We only have barely enough Cola for a Coup de Burst, so we're holding out for an emergency."
Chopper nodded slowly. "Yes, but- how would that account for Luffy's lethargy? We're all only eating that much every day, and he's the only one who- "
"But he's rubber."
But what does that have to do with it?
The doctor sat down in his chair hard, mind buzzing. Luffy stretched all the time; to fight, to climb, to fish, to play, to eat. It was probably second nature, and felt no different than moving like a regular human at this point, especially if he'd eaten the fruit when he was very young the way Chopper thought he might have.
And when he ate so much his belly got big, he could compress that food, and move the nutrients to the parts of his body that ached or needed healing, and it helped him feel better faster. His metabolism must be fast- really, really fast.
Everything he does, Chopper realized in dawning amazement that felt more like horror, burns five times as many calories as when we do it.
"He's starving!" Chopper wailed, and leapt from his chair. It went spinning across the room, and as he ran out the door, Zoro didn't move.
Chopper breezed past Nami and Usopp, who lingered in the hall, and slammed into the kitchen at full speed.
"Sanji!" the reindeer gasped, waving his arms at the chef to get his full attention, despite the fact that the man was already turned around and staring at him. "Sanji, I need you to make a broth! A thick one! Right now!"
"Chopper?" the blond man moved forward like he would come and kneel beside him, and Chopper wanted to growl at him like a real beast. "Are you- "
"He has no energy because he needs to eat," Chopper snapped, and did his best to sound very demanding but it came out like a plea. There was no need to clarify who 'he' meant, either, from the way Sanji's eye narrowed a bit. "He needs more food than the rest of us cause he burns through it too fast, but he hasn't been eating as much- "
He had to pause to inhale with a wheeze, but he didn't have to say anything more; from the sickly, pale pallor of Sanji's face at that point, the cook understood.
Sanji turned away sharply, putting his back to the room and the doctor and the whole conversation, but he slammed a pot down on the stove and Chopper knew he'd have the soup as quickly as Sanji could make one.
"Damn him," he could hear Sanji muttering tersely under his breath, sounding ragged and upset. "Damn him, damn him."
Chopper sank against the bench seat by the table, trying to catch his breath, and his hoof was shaking when he pressed it to his chest. He wanted to be angry at his captain, he really, really did, but he knew exactly what Luffy was thinking when he decided not to tell.
"I'm the captain! If my nakama can't eat, neither will I!"
He probably didn't even realize it was a question of metabolisms and blood sugars; he would only think it was a matter of being hungry.
When they returned to the office, Sanji was clutching a bedtray in steady hands; but his grip on the handles was white-knuckled. Zoro cast a glance up at them when the door opened, but he didn't seem in any hurry to move.
He looked really hard at Sanji for a long minute, with Chopper looking between the two of them as he hopped up on the other side of the bed. Sanji's face was all dark and angry, but his eye that Chopper could see looked electrified and scared.
After a minute, Zoro said, "You didn't know."
Sanji flinched like he'd been struck, even though it sounded like Zoro was trying to make him feel better, and his gaze fell to the floor. Zoro shook his head and stood, gathering all his swords at his hip and securing them there. He lingered at Luffy's side a moment longer, before he gave up his spot and left.
"Put the tray down there," Chopper said, indicating the desk. He shook Luffy by the shoulder gently. "Luffy- I know you just went to sleep, but you need to wake back up. Just for a little bit, Luffy."
His poor captain, quietly sleeping away the days; his poor body, doing its best, as always, to keep him alive.
Luffy shivered, and his eyes opened an inch at a time and he sat up just as slowly. The usual bright brown was muddy, and the hand he lifted to rub his face was shaking. Sanji inhaled sharply, and Chopper wondered if it was even a good idea to have him in the room.
"What the hell is wrong with you," the cook whispered, and for all that he looked furious, his voice was thick like he was going to cry. Luffy looked at him, and when Sanji reached out Chopper was on the wrong side of the bed to stop him-
But he didn't grab him, or hit him, the way the reindeer thought he would. Instead, Sanji cupped Luffy's head in his hands, fingers curved around his jaw and his neck, and just looked at him.
"What is wrong with you," Sanji asked again, with only a tiny bit more strength in his voice. "Why didn't you tell me you were hungry?"
"We're all hungry," Luffy said, and Chopper drooped.
I was right.
"But you're the only one dying!" Sanji snapped, and the dam behind the fear-fury-shame in his face broke and everything flooded out. "No one's been able to do anything with you laying in here, sick and quiet, and this whole time I could have helped you. You were starving, right down the hall from me, and I was just letting you starve- "
He broke off, because Luffy's hand reached out for his- reacting automatically to his nakama's heartbreak. And even in his anger, Sanji closed the distance and wrapped his fingers around his captain's firmly.
"I can't let you go hungry," Sanji told him firmly, the way Zoro repeated back Luffy's orders before a fight, the way the moon told the ocean to turn tides. "I can't, Luffy."
It was logic an outsider might not understand, but it made all the sense in the world to Chopper; the same way he couldn't turn away a patient, the way Nami couldn't turn away a child, this was important and fundamental, and Sanji would hurt forever if Luffy didn't eat.
And Luffy must have seen it, too, as he stared at Sanji staring back at him; because he sank a little, crestfallen, and murmured, "Sorry, Sanji."
Sanji put his free hand in Luffy's hair, and Chopper leaned a little closer. The hardest battle had been won.
"In a little bit, I'll explain to you about what makes your body different," the doctor said, patting Luffy's arm gently. "But for right now, you should eat. You'll stop feeling sleepy and cold if you do."
"And we'll share this with the others, too," Sanji continued, filling a bowl with the soup and setting it in Luffy's lap before the rubber boy could come up with any argument. He took a seat in the chair by the bed, and settled in for the long run. His face was still pale and there was something electric in his eye, but when Luffy picked up the spoon and took the first bite, tension bled off his body like rainwater. "I think we've waited long enough to use the Coup de Burst. We'll fire it up in the morning, after everyone eats a nice dinner. After you eat a nice dinner. Good, captain?"
Luffy nodded, eyes only half open, jaw working mechanically. He was halfway through the bowl already, and Chopper watched his trembling hands like a hawk. "S'good, Sanji."
Sanji leaned back in his chair, clasped his hands, and whispered, "Good."