Dark like the North Blue Sea (aka The Sea-Hill you Die On)

"And then he said it was a sea-hill." Usopp snapped an elastic band against his wrist. Kabuto was always close, but it was hard to practice in the confined spaces of the Polar Tang. Too many nuclear reactors at hand or some other Occupational Health and Safety bullshit.

Penguin sat across from him, peering out from under his cap, arms folded. He turned to Shachi, the cook of Law's crew. "Sea-hills? You see them all the time."

Shachi, mug of coffee at mouth, nodded. "Nothing unusual."

"You do not!" Usopp shouted, then calmed down. "We've sailed a lot, and we never saw a sea-shaped hill until we sailed between Punk Hazard and Dressrosa."

Shachi and Penguin looked at one another again. What counted as a lot?

"Common in the North Blue," Shachi said. Law was at sea from age ten. And both Penguin and Shachi had lived on the coast, their parents falling victim to a freak tidal wave.

Usopp wished he had Nami to ask, but she was off rescuing Sanji and keeping Luffy out of trouble in the face of Big Mom's— inevitable-as-a-skull-joke—wrath. He shivered as if Brook had just trespassed upon his very soul, and—although he felt a little guilty—was pleased to be within the safety and warm walls of Law's submarine. Very warm. He swiped at the back of his neck, and his fingers came away wet.

He wasn't getting anywhere with the sea-hill, but Shachi and Penguin were easygoing, and Usopp enjoyed their company as they all shared stories about their far-from-cautious captains. He changed tack.

"He said that a fighting fish was a fish!"

The Heart duo glanced over as one.

"Isn't it?" Shachi asked. He was a bit jealous. Usopp had fought alongside Law. But he was also a little relieved that he'd avoided some of the danger.

Usopp, waggled two fingers at the top of his head, snorted, and turned his head from side to side. Penguin lazily flapped one of his hat's ear coverings. The Strawhats really were something.

"It's like a bull and eats through steel girders and's as large as a sea king."

"That's a fish," Penguin said. "The sea king."

"Next you'll tell me that a whale is a fish," Usopp said.

At the end of the table, Ikkaku tinkered with the mechanics of a valve with a faulty dial. She picked up a small screwdriver and spoke without looking over. "A whale is definitely not a fish."

"She should know," Penguin said.

"Dolphins neither," Shachi butted in.

"He should know."

The Hearts should know.

"The topic at hand is fighting fish and sea kings, is it not?" Robin sat in a very comfortable armchair in the corner. Law had rummaged through his own quarters to locate it. Favouritism or what? Though the crew usually liked hanging out on the bench seats in the mess. Like now.

Franky had designed holders for drinks and books, not that Robin needed them. But, beverages could burn or freeze her spare hands, so it was appreciated.

"Yes!" Usopp winced as he thwapped the rubber band a little too vigorously against his skin. "They were gargantuan. And never mind whether it's a fish or not. Your captain—Mighty Warlord of the Sea—couldn't fight. Some stamina thing. So I—" Usopp slapped his chest "—The Fearless Captain Usopp, defeated those hideous beasts, single-handed."

Shachi and Penguin rested their chins in the palms of their hands, elbows on the edge of the table. Warlord of the sea. Ouch.

"He's a real slackarse at times."

"Mhmm."

One of Robin's devil-fruit hands twisted Usopp's cup so that it was easier for him to pick up. He coughed. "With a little help, of course. Though not from Law."

"We read the papers. Looks like you did a good job."

Usopp grinned. "Your captain called me God."

"You really ruffled Doflamingo's feathers." It took some doing. They were impressed

"The navy admirals must be on the lookout for you now," Ikkaku murmured to the device in her hand.

Bepo, left of Shachi, sighed and Shachi patted his arm fur. "It's better to lay low," he whispered.

Usopp's ears prickled and his drink, hovering near his mouth, shook in his hand. Robin smiled. He'd never learn.

Usopp rose from the table, the mug now wobbling on the surface. "It's a matter of great urgency that I patrol this ship. Never fear—" He pressed his hands down onto the wood. "Intruders will quake in my presence."

All Hearts stared at him, then back to their mug, or mechanics, or book, or conversation. No skin off their noses. Usopp left the room.

Shachi turned to Penguin. "What's a sea-hill?"

"Fucked if I know," Penguin laughed. "We sail under the ocean, not on top of it."

"Fighting fish really are quite monstrous," Robin added, looking up from her book, holding her finger on a word so she wouldn't lose her place.

"But a fish," Ikkaku said, finally getting the dial to smoothly turn the way it should.

"Granted," Robin replied.

"I mean, I don't need to be a god," Bepo mumbled, "But something better than a mascot."

"You're our secret weapon, Bepo." Law walked into the room, a sheen of sweat across his forehead, as with all of them on the sub.

"We'd be up shit-creek if the navy admirals targeted you, if they realised you can navigate the sub in all conditions to anywhere." He took the seat that Usopp had vacated. "You're the heart of the Heart Pirates."

Bepo ran his paws and claws across the table top, a toothy-fanged grin splitting his face. He knew that Law's mentor was the real Heart, but Captain's praise could be sparse and was all the sweeter for it.

"Stop." Ikkaku couldn't concentrate with the screech of claw to lamination.

Bepo slumped to the surface, but Law shambled a cup from the counter and it clunked in front of him. Bepo wrapped his paws around it, the contents lukewarm, (Franky had thought he was doing them all a favour by making drinks for the crew, not quite having figured out their shifts), and felt a little better.

"Usopp said that he took out the fighting fish when you were in Dressrosa, and that they were monstrous beasts." Shachi took a sip of Bepo's tea after he'd placed it back on the table, and grimaced at the floating leaves. Didn't the Strawhats know how to use strainers?

Law nodded. "Yep. Nico-ya, God-ya and Caesar took care of it."

"And that they were not fish."

"I'd call them a fish." Law shambled in another luck-of-the-draw mug-of-something for Bepo to waylay another meltdown.

"That's what he said."

Law shrugged.

Penguin stirred the sediment of cocoa and sugar towards the bottom of his drink, the teaspoon hitting the side of the china.

"What's a sea-hill, Captain?"

A small smile crossed Law's face. "Fucked if I know." He shambled Usopp's mug to the sink, wiped at the water stain with the edge of his shirt. "But in all of the world's oceans, it's common knowledge. You see them all the time."

A/N: Based on Law's comment to Usopp in Chapter 698 while they're on their way to Dressrosa.