"Hey, what's THAT?!" Luffy's exclamation rang out. Usopp looked up from his fishing to see Luffy hanging upside down from Merry's head by his legs, staring at something under one of her curled horns.
After a brief glance to see if anyone else could be bothered to attend their captain's question, Usopp got off the rail and went to investigate what had caught Luffy's attention.
"Look, Usopp." Luffy caught him by one overall strap and yanked him halfway overboard. Usopp flailed a moment before catching Merry's neck, and hung by one arm and Luffy's grip on his overalls. He glared at Luffy, then looked up and saw what Luffy was looking at.
A chrysalis was stuck to the wood in a cranny well-protected from wind or rain. "See?"
"It's a butterfly, Luffy."
"But there's no wings." Luffy sounded confused. Usopp twisted to look at Luffy's upside-down face.
"Well, it's not one yet. It's the between part, after the caterpillar."
"That's gonna turn into a butterfly?!" Luffy's eyes widened, and he grinned, reaching up for it. Usopp smacked his hand away.
"Oi, oi! You're gonna crush it or something. You're too strong to touch that, it's really fragile."
Luffy jerked his hand back, . "Like those fancy sugar thingies Sanji makes for Nami and Robin?"
"Yeah. Except he can't make you another one if you crush it, it'll just be dead." He squinted at the chrysalis, trying to identify which butterfly it could be, but shadowed under Merry's horn, he couldn't see much to identify it.
"Then be careful!" Luffy admonished him, and before Usopp had time to be indignant, Luffy had launched him back onto the deck.
"You're the one who can't be careful!" Usopp shot back.
"Quiet! I'm guarding my butterfly!"
The next few days were uneventful, no rough seas or attacks from Marines or other pirates. Nami completed a section of her map, Zoro did ten thousand more pushups on top of the mast, Robin read a lot, everything was normal. Except Luffy, who spent every waking moment perched on his special seat like a skinny, rubbery gargoyle, watching every angle for imminent danger to his self-appointed charge under Merry's horn. Usopp came out for watch one night to find him asleep on the figurehead, lashed fast, most likely by Zoro, to prevent him falling into the water. One arm was slung protectively over the place where the chrysalis hung.
They stopped at an uninhabited island on the sixth day after Luffy had found their insect stowaway, and that evening, after they'd dealt with the woman they encountered who was fleeing a group of pirates who'd followed her to this island, but who turned out to be loyal crewmembers trying to rescue their boss-lady from a poison-induced amnesia, Luffy dragged Usopp up to the figurehead for his daily status report on the chrysalis.
Usopp did what had become routine, inspecting the chrysalis through his goggles and using one of Chopper's stethoscopes to listen closely to the wood around where the chrysalis hung to discover how the developing inhabitant was doing. Each day he got a different result. "Oh, now this is becoming clear, why didn't I see it before! This isn't the eight-winged vampire butterfly at all, it's obviously the extremely rare--and extremely dangerous!--lightning butterfly! I fought off a plague of these when I was just three years old, but not after they reduced all the neighboring towns to rubble! If a thousand of them gather together, they create HUGE lightning bolts that can burn up whole forests."
"Whooooooooaaaaa, that's so cool, Usopp!!"
"I know, I know, Captain Usopp is indeed the most knowledgeable about all insects."
The reunion party for the temporarily-lost captain and her crew went on long into the night. Usopp eventually fell asleep next to Luffy at the base of the figurehead
He awoke sprawled on the deck, Luffy's shoulder no longer his pillow, Luffy in fact gone from his side altogether. The sun was peeking over the water, and Usopp scrubbed at his face, wishing he'd picked somewhere less picturesque and more sleep-enabling to pass out.
"Hey, Usopp," Luffy's voice carried down from above in a highly uncharacteristic whisper. Usopp peeled himself off the deck and got to his feet, rubbing his eyes with his fists.
"Nn?" He yawned.
"Look!"
Luffy was cross-legged on the figurehead, but he sat sideways, hands planted on his knees, peering sadly downwards. Usopp climbed onto the rail to lean up over Merry's neck and see what Luffy was looking at. Just by one of his feet a soft-looking, crumpled-winged butterfly was creeping over the curve of Merry's horn.
"Oh, it came out," Usopp smiled.
"It's squashed," Luffy said, and his voice was tearful. "But I didn't touch it. I really didn't."
"Oh, no, Luffy, it's fine," Usopp reassured, looking up at him, "you protected it, and it's fine. Its wings just have to dry out now. It will sit still for an hour or two and then it'll be ready to fly."
"Oh..." Luffy had his lower lip between his teeth and he reached down. Usopp gritted his teeth against a reflexive reprimand, and watch Luffy put his hand slowly palm-down on the horn, in the butterfly's path.
One tiny leg at a time, the insect climbed onto the back of Luffy's hand. "I can hardly feel it," Luffy marveled. He carefully moved his hand onto his lap. A breeze passed over them, tugging at the butterfly, but it clung fast until the air stopped moving, then began moving again. "Where's it going?"
"They usually hang on the side of things while they wait," Usopp replied. "Here, maybe..." He reached over and took Luffy's hand, careful of its passenger, and shifted it to rest against Luffy's stomach.
The butterfly moved onto Luffy's vest, its new body now hanging vertically, and stopped next to one of the gold buttons.
When Usopp looked at him again, Luffy was smiling widely. He shifted carefully, turning his back to the direction of the intermittent breezes, and letting the sun fall on his front. "Safe," he said, and glanced at Usopp with a radiant grin.
The sun rose, the crew slept, and Luffy sat almost perfectly still as the butterfly's wings dried. Usopp sat with on leg over the rail just below, and told Luffy all about the adventures of a talking butterfly he'd once encountered during his trip to the north pole.
"Ah, you want to fly?" Luffy said suddenly, a minute or so after the tale about the talking butterfly falling in love with a beach umbrella was done. Usopp got up again to look. Sure enough, on Luffy's chest now hung a golden-orange and black butterfly, like he'd been pinned with a bright badge. Its wings slowly opened and closed, ready for flight.
Usopp laughed a little. "You know what this is, Luffy? It's a monarch butterfly. It's the king."
"No wonder it came to be with us," Luffy said, delighted.
The island they were at was a summer island, and Usopp had seen, between bouts of frenzied chasing, fleeing and fighting, a few monarchs fluttering through the clearings of the forest.
The one resting on Luffy took off at last, rising above them for a moment, and beginning its first flight down along the ship. After a couple of moments watching it dip and rise, Luffy vaulted down from the figurehead to follow it.
It fluttered the length of the ship before a breeze caught it and sent it over the water between them and the shore. Luffy hung over the aft railing and stared, still watching even long after Usopp had lost sight of it among sun-brightened foliage.