Sanji was sick. Zoro was certain that the blond had always been mentally ill, but now Chopper had confirmed that the ship's cook was suffering from a highly uncomfortable disease that, essentially, meant he would be stuck in bed, in quarantine what was more, for at least two weeks. No way he was cooking anything.
Luffy was, understandably, forbidden from the kitchen. Usopp, they quickly learned, had a habit of burning anything he tried to cook. Nami knew how to make all of three dishes, and she was the only one who liked two of them, apart from Luffy, but he ate everything. Vivi, being a princess, had never needed to learn how and was more likely to cut off a finger than correctly chop a vegetable. Chopper was too busy tending to Sanji to also cook three meals a day. By process of elimination, that left Zoro to take over the chef's kitchen duties. To make sure he actually cooked, Nami held on to the key for the liquor cabinet.
He spent a day in the kitchen searching cupboards and pantries, just learning where everything was, and before he started cooking anything, he read through the entire recipe in the cook book he had found and laid everything out on the counter that he would need. Luffy, thankfully, didn't interrupt him there as the boy had made a habit of doing with Sanji. He had made an attempt the first day of Sanji's illness, but Zoro had been there, swords ready to defend the pantry and cold-store from the hungry captain. On the second day, Zoro had explained to Luffy that, if he wanted to actually eat something that tasted even vaguely good, he would stay out of the kitchen and out of his way, or no one would be eating anything.
Between the cooking and the cleaning up of meals, Zoro had taken to doing his training in the kitchen. Sometimes he even strapped his weights to himself while he did what was normally Sanji's job. The kitchen was quiet, without the cook or a hungry Luffy, and as long as he was in there, nobody bothered him to do anything else. They all just started to take it for granted that Zoro was doing something food related in the kitchen and it was better to not disturb or distract him if they didn't want him to – deliberately or accidentally – burn their food.
It was three weeks before Chopper declared Sanji no longer contagious and well enough to get out of bed, but only for short periods of time. The cook was still too weak from his illness to be quite up to cooking, though the blond was determined that he could at least prepare everybody a snack – something that they had all been going without since Zoro had been the one in the kitchen. Not that Sanji had known. Zoro had – as per Chopper's request – made special rice balls for Sanji to eat between meals every day, with his medicine stuck in them along with whatever filling Zoro added.
Another week passed before Sanji was well enough to return to his kitchen full time, and Luffy was back to trying to sneak into the kitchen for meat.
"How did you keep him out?" Sanji asked Zoro one day as the swordsman helped wash the dishes. He hadn't been asked to help, but he'd gotten up from the table and simply out of a habit three-weeks trained into him, started taking the used plates to the sink.
"I threatened bad food for him, and then no food for anybody, if he kept trying to sneak," Zoro answered. "That I would have sliced open his palm, rather than kick him in the head, may have had an effect as well."
Sanji was appalled, but nodded his understanding.
"Thank you for doing this Zoro," Sanji said quietly. "For doing my chores while I was sick, I mean."
Zoro shrugged. "No problem. It was actually kind of fun," the swordsman said. "Oh, and I sharpened all of your knives for you," he added. "If you respect your blades, they'll do better work for you."
Sanji nodded his silent appreciation. They stood side by side in silence until all the dishes were clean again, and then Zoro helped put everything away before leaving the galley for his shift in the crow's nest.
Hand on the frame of the door, he stopped and looked back over his shoulder.
"It's good to have you back, ero-cook," he said, a one-sided grin on his face.
"Thanks Marimo," Sanji answered, a smirk on his own. "It's good to be back."