Title: Sansen Sekai (Three Thousand Worlds)
Summary: They say that death is final, but no Strawhat would accept that without a fight. Now Zoro and Robin must struggle through a bewildering maze of alternate universes in order to survive with their memories, their selves—and each other—intact.
Spoilers: The real/living-world portion takes place before Water 7, but spoilers for Robin's past.
Warning: I may have been on crack when I wrote this. This is basically a series of bizarre what-if AUs. Proceed with caution.

"Usopp, how many lights do we have left?"

Usopp drew himself upright and squared his shoulders, which made no difference since Nami couldn't see him in the dark. "The great Usopp-sama does not use his Sure-Kill Flame Stars to light candles," he proclaimed, raising his head proudly.

"As far as I know, the great Usopp-sama can't see in the dark either," Nami said, sounding scarily patient.

"C-Captain Usopp is used to dealing with difficult circumstances!"

"Just answer the question already, or I'll show you difficult circumstances."

"Yes ma'am," Usopp said quickly. "I have five more Flame Stars in my bag. I also have a rubber band."

Nami nodded, considering their options. It was sheer luck that Chopper had been carrying a box of candles when the ground had collapsed beneath them, but it looked like their luck was running out—or at least the candles were. She smoothed a finger over the waxy cylinders in the dark. No matter how many times she probed at the edges of the box, she hadn't been able to find a single hidden stub of a half-spent candle. They only had eight left, and one had a bad wick. If they were careful about avoiding drafts, they could light candles with other candles, but that was only still at most sixteen hours of light before they were plunged into a darkness that already seemed very final.

"We'll conserve our resources for now," Nami decided. "Once those idiots get a hold of themselves, we'll try again."

There was no question as to which idiots she was talking about. Sanji had succumbed to weeping quietly in the corner, flicking his spent lighter repeatedly and mumbling about he had failed Nami-san. If only he had a spare lighter! If only he could kick through solid rock! If only he could cook a nutritious and filling meal out of dirt and pebbles! He was a failure as a cook, a man, and as Nami's candle-lighter. Ahh, if only…

He had picked up this line of self-flagellation when Zoro dropped it earlier, in favor of sleeping. It had been a while since Nami heard the swordsman grumbling about not being able to cut everything he needed to, about his katana not being sharp enough. Instead, the cavern was filled with the oddly soothing sound of snoring.

The lazy bum could sleep anywhere, Nami grumbled to herself, and navigated by feel over to the far side of the cave, where Robin had promised to occupy Luffy. Their captain was the biggest idiot of all. He had so much energy it was ridiculous. When he wasn't running back and forth in the limited confines of the cave, he was banging his head against the wall, screaming something about "gomu gomu no woodpecker!"

In that regard, Robin worked miracles. Nami now gazed in her general direction as one might gaze at a descending angel. Luffy was, well, being quiet!

"How is he doing?" Nami whispered, coming to a stop. There was the vague impression of someone in front of her, though she could see nothing.

"Captain-san is fine," Robin said. Nami could hear her smile even in the gloom. "We're playing a game. Doctor-san is here too."

"A game?" Nami asked.

"Yes. Doctor-san and I are tying Luffy's fingers and toes together. He's trying to get them apart. It's a race, I guess. Would you like to join?" Robin's hand found Nami's, and pressed into it something warm and pliant. It had the feel of rubber stretched beyond its limits. Nami let go at once, and heard it snap a foot or two away.

"Ow!" said Luffy, the first word he'd spoken in hours. Nami supposed that a miracle was still a miracle, even if she really wished she hadn't asked how it was done.

She crawled back, murmuring something encouraging and appreciative.

There was another snap, and then the sound of Chopper giggling.

"Hey, that's cheating!" Luffy said.

Nami didn't want to know.

"There's a sign! Guys, there's a sign! Stop!"

Sanji skidded to a halt. "YES, Nami-swaaaan! Whatever you say!" He was eager to make up for his lighter failure.

"Usopp, bring the candle closer. I can't read it."

"What's this creepy underground lake?" Usopp wondered as he did so. "I have a bad feeling about this."

Robin knelt by the sign, curiosity piqued. Luffy followed her, grumbling something incoherent. In the candlelight, Nami could see that his fingers had been stretched over his mouth and tied behind the back of his head. She thought about untying him, but he didn't seem to be in too much pain.

"What's it say, Robin?" Chopper asked eagerly, running up behind Luffy. Zoro brought up the rear, one hand on the hilts of his swords, the other rubbing tiredly at his eyes. He had clearly just woken up.

"This lake is death," Robin said, in that quiet way of hers.

Usopp dropped the candle, which plunged wick-first into the lake. The cave was dark and silent as the whole crew took this in.

Then:

"USOPP, WHAT'RE YOU DOING, THAT CANDLE WAS PRACTICALLY FRESH!"

"HOW DARE YOU UPSET NAMI-SAN! I'LL BREAK YOUR LONG NOSE, YOU LONG NOSE!"

"DON'T BLAME ME, SHE SAID IT WAS D-D-DEATH!"

"IS IT REALLY DEATH, ROBIN? ARE WE GOING TO DIE?"

"SHUT UP!" Nami yelled. She took a deep breath, preparing to yell again, but it wasn't needed as the others quieted. "Usopp, another Flame Star. Hit me and die. Actually, Sanji-kun," her voice dripped honey, "why don't you hold the candle for him?"

"Of course, Nami-saan!" Nami felt for Sanji's hand, and pressed their last candle into it.

"Got it. Usopp, I'm holding the candle to the right of my head. Hit Nami-swan and die."

"Uh…" Usopp swallowed loudly. "Robin, are you doing that?"

"Doing what?" Robin asked.

"Someone?" Usopp's voice cracked. "Is someone touching me, or does that cold, slimy tentacle curled around my ankle belong to a scary lake-monster that's about to eat me alive?"

"There are scary lake-monsters?" Chopper screamed.

"Hurry up and light the candle already!"

Usopp let out a cry as a plume of flame shot forth from his slingshot. It momentarily illuminating his pale, horrified face and the way his eyes were squeezed shut against what nightmares might await him should he open them. In the next moment, Sanji flew forward, lit candle held aloft, to aim a swift kick to the tentacle extending from the lake. Three hands reached out of the ground to grab Usopp as he was nearly flung in after it, and the tentacle finally released its hold on his ankle and sank back into the water's depths with a slurp.

"What the hell was that?" Zoro asked, swords out.

"Nami-san, Robin-chan, did you see that?" Sanji chanted happily, dancing circles around the two girls.

"The Guardian of Death," Robin read. She was kneeling by the sign again, ignoring Usopp's kneecaps, which were trembling bare inches from her face. "The Keeper of the Way. The Grim Reaper, if you will."

"No way!" said Chopper. "The Grim Reaper is an octopus?"

"Whatever it is, I'll cut it up," Zoro announced. "No way it's going to get away with attacking us from underneath, in the dark."

"I don't think it meant us any harm," Robin said, to a chorus of incredulity. "It merely thought Usopp was the toll."

"T-t-toll?" Usopp stammered, teeth chattering.

Chopper looked up at him in horror before thinking to wonder, "What's a toll?"

"Some must pass into the Lake of Death for many to escape the Cavern of Despair," Robin read.

"Well that stupid octopus had better get up here so I can put my Foot of Death into his Face of Shittiness. Then we'll see about Despair," Sanji added, lighting a cigarette on the candle he held and blowing a ring of smoke.

"This is a serious matter, Cook-san," Robin murmured. "According to the sign, there is no way out of here unless one of us dies."

"What?" Usopp dropped his slingshot, which Chopper hurriedly caught for him.

"Good thing that wasn't the candle," Nami muttered.

"No way."

Everyone turned to look at Luffy. He had managed to get his hands out of his mouth, but most of his fingers were still tied behind his back.

"Captain-san?" Robin asked.

"There is no way I'm losing any of my nakama. No one's going to die."

There was a rippling on the surface of the lake. A low groan emanated from the water; its echoes filled the cave, humming and buzzing in their bones.

"No!" Luffy snapped, shooting an authoritative glare around his stretched-out fingers and slightly flattened face.

The answering groan was petulant this time.

"No means no!"

"Look," said Robin, pointing up. "Look at the smoke."

All eyes followed the smoke from Sanji's cigarette. It trailed into the air, followed invisible currents over the lake, and then… stopped.

"Where did it go?"

"There!" Usopp turned, and pointed at the wall directly behind them. A distinctive row of smoke rings emerged from the wall, rose up, and dissipated about the ceiling.

"Whoa, that's so cool!" Luffy exclaimed. He ran for the wall in question, fingers still tied behind his head, and disappeared from view. His voice echoed over from the other side of the cave. "That's awesome! Guuuuuuys! Can you see me?" From across the lake, Luffy gave them his best attempt at a wave, which involved shaking his entire upper body back and forth.

"How did you do that?" Chopper gasped. He looked a little scared and a little like he wanted to try it too.

"Dunno, but it's awesome!" Luffy turned around and ran back the other way. A second later, he walked back out of the wall on their side of the lake, and collapsed down into a happy little pile. "Phew! What a great cave! I want one!"

"As the sign says," said Robin. "The cave is limitless. If you walk to one end, you merely appear again at the other."

"I see," said Luffy, who didn't. "A mystery cave."

"Then… how do we get out?" Nami asked.

Robin didn't answer, though her eyes flickered over to the lake. "Death wouldn't be so bad," she said, which Nami knew was her version of an offer.

There was a loud snap as two of Luffy's fingers came untied. He marched over to Robin stretching his neck to put his face right in front of hers. "What do you think you're saying! I'm the captain, and I already said no!"

The tentacle swept Robin off her feet. Rather than plunging back into the lake, it held her suspended over it like some sort of demented marionette.

"Robin can't swim!" Chopper squeaked, running over to the lake in preparation for rescue. Then: "I forgot! I can't swim either!"

"PUT DOWN ROBIN-CHAN!"

"Don't come! Cook-san, stop! The lake isn't water! It doesn't matter if you've eaten a Devil's Fruit or not, you can't save me. Stop! Someone stop him!"

"But Robin," Nami hesitated. "We can't just let you…"

"Stop Cook-san! Get out of here." The thing pulled Robin down to the surface of the lake. "As soon as you touch the lake, you'll die! It's too late for me. Get out of here! DON'T YOU DARE COME FOR ME."

The last was a scream. They had never heard her scream before. Even Sanji hesitated. "Robin-chan," he whispered. And then she was gone.

The surface of the not-water was unnaturally still.

"Robin…" Luffy breathed, disbelieving.

"That shitty squid!" Sanji yelled, running for the lake, steps punctuated by his furious raving. "Taking advantage while I was distracted! I'll kick it until it's flat! I'll kick it until it's see-through! I'm coming, Robin-chan—"

Sanji collapsed. Nami folded up her Clima Tact and looked down at Sanji to make sure he was unconscious. When she looked up, her eyes were suspiciously bright, but her voice was steady. "We have to come up with a plan," she announced. "It's not going to help anyone if we just rush in and get ourselves killed."

"ROBIIIIINN!" Luffy yelled. His voice came from very far away. This was because he had attached his feet to the signpost and stretched his legs as far as they would go. He looked like he was ready to catapult himself into the lake, despite the fact that his hands were still tied over his head.

"You idiot! What did I just say?" Nami stomped on Luffy's ankle, insofar as any part of the stretched-out leg could be identified as an ankle. Yelping, Luffy let go. There was a snap as another couple of his fingers came free.

"Th-th-that's right!" said Usopp, who was kneeling over the lake now. He and Chopper wore matching expressions of horror on their faces. "We have to… we have to think about this. Calmly. Robin… Robin said…"

"Not to go after her," Zoro finished. He didn't mind having to bring up the difficult subjects. "If she sacrificed herself so we can get out…"

"We're not leaving Robin," Luffy announced flatly.

"She might be dead already," Zoro stated, just as calmly.

"We're not leaving her!"

"Something's coming."

They all turned to look at the lake, which writhed with bubbles. A huge whirlpool was forming in the middle, and before their eyes, a woman rose into the air. She was undeniably beautiful, with her skin unblemished and her unadorned hair forming perfect cascades over her shoulders, except for the fact that her arms and legs ended in—

"Tentacles?" Chopper yelped.

"Sanji would throw a fit," Nami muttered, then added in a louder voice, "Who are you?"

"GIVE BACK ROBIN!" demanded Luffy, and drew back his arm to attack.

Zoro glanced at his captain briefly before drawing one of his swords. "We won't pay this toll." He stepped up beside Luffy, forming a picture of solidarity, as though he hadn't been arguing with him a moment before. In his mind, he hadn't.

"Your nakama is already dead," the woman said, in a voice like oozing slime, "but she was not the toll."

"What did you say?"

"The woman was an acceptable sacrifice, but the toll still must be paid."

"Talk sense, octopus!"

The octopus-woman pouted. "I don't get you people! Back in the day, people actually understood the ritual. A willing sacrifice to summon me, and an unwilling toll to pass through the gates. Nowadays people just barge in here with no idea how to go about things. Don't you get it? Two people! I need two people! Otherwise you're never getting out of here."

In the silence, everyone turned expectantly to Luffy, waiting for the inevitable furious explosion. Instead, Luffy grinned. "All right, then… I'll die!"

"LUFFY?"

The woman looked at him suspiciously. "Aren't you the captain?"

"Yup! I'm Luffy!"

She sighed. "Why do you people never read? At least your nakama managed to get the first part right. Now the captain (that's you) has to force one of his crew (that's one of you five) into the lake. Then the rest of you can go."

"So… I can't be the other sacrifice?" Luffy asked.

"The toll," she corrected testily.

"The captain can't choose himself?" Luffy pressed.

"That's right."

"Then… it'll be Zoro!" Luffy said cheerfully, and pointed at his first mate.

"Lu-Luffy," Nami stammered, horrified despite herself. Sacrificing himself was a stupid idea, but an honorable one. Singling out one of his precious nakama to die was unthinkable. "What are you doing? I thought you said you weren't going to leave any of your nakama behind?"

Luffy merely gave his blithe grin and continued to look pleased with himself.

"Luffy, how could you?" Usopp asked, stepping towards him. He took a deep breath, steeling himself. "There's no way I can accept this! The Great Usopp cannot stand by while you kill one of your nakama."

"Usopp," said Luffy, grin suddenly disappearing. "What would you do if I chose you?"

"What?" The color drained from Usopp's face. He took an involuntary step backwards. "I… I guess I'd understand. I'm not the best fighter, and I don't repair Merry very well. If it's for the crew—"

Luffy turned his head. His gaze passed right over Sanji's prone form. "Chopper. What would you do if I chose you?"

"M-me? I…" Chopper looked around, terrified.

"Luffy, stop that!" Nami stepped in.

"Nami," said Luffy. "What would you do if I chose you?"

Nami froze. He wouldn't. But… She looked over at Zoro, who was watching the goings-on with that stoic calm of his. Of course he never went against his captain; for him, it seemed natural as breathing to follow along with whatever Luffy decided, without question, without concern. But even so, he couldn't be willing to die for his captain's whim. Didn't he have dreams? Nami considered her response with care. If she protested too much, would Luffy really sentence Zoro to death? Would he go that far? Could she really choose her own life over his? "I… I'd do it," Nami began hesitantly.

"Zoro!" Luffy interrupted, that blithe grin returning to his face as he turned to face Zoro. "What would you do if I chose you?"

Zoro met Luffy's gaze calmly. Zoro won't die, Nami thought breathlessly. He won't just passively accept this. Not even from Luffy.

"Zoro?" Luffy prompted.

And Zoro grinned too. "If you did that, Captain, I'd kick your ass. I wouldn't care what it took—I'd come back from death itself just to beat you up. And I'd bring Robin with me too, while I was at it."

Luffy and Zoro grinned at each other for a while.

"Don't be stupid," Nami shook her head. "You can't come back from death."

"Watch me," said Zoro.

"It's death!" Usopp said. "It's not like getting kidnapped, or lost. When you die, that's it! You can't come back, no matter how much you want to."

"How do you know?" Zoro asked. "You ever tried it?"

Luffy's last few fingers came undone with another snap.

"Nami and Usopp are right. Not even I can do anything if you die," Chopper whispered, awed despite himself at Luffy and Zoro's coolness.

"Anyway, you'd better hurry. See you later, Zoro!" said Luffy, and punched Zoro in the chest, hard.

"Yeah, yeah. I'll be back, Luffy!" As far as shocked and betrayed curses went, it sounded rather half-hearted. "I'll never forget this!" he added, one hand on his swords, the other hand forming a fist that he shook vaguely in the air.

"Zoro, wait…" Chopper called, slightly desperately. "Don't you want us to hold your katana for you?"

"Are you kidding?" Zoro asked. "How am I supposed to fight my way back from death without my swords?"

There was a splash, and he was gone.

"Well, let's go," said Luffy cheerfully. "I'm hungry. I hope Sanji wakes up soon."

"Aren't you worried about Zoro?" Usopp asked, still staring at the spot the swordsman had occupied just a moment ago.

"Well, he'll probably hit me when he gets back, but he won't kill me," Luffy shrugged. "That'd be mu-ti-ny."

"That's not what I meant," Usopp muttered. A huge vortex had opened in front of them. There was a light in there, somewhere in the distance.

"I'm not worried at all," said Luffy, scooping Sanji up. "He'll be back. He'll bring Robin too. It's Zoro."

"Even if it's Zoro," said Usopp.

"He still has to become the world's greatest swordsman!" Luffy said. "Sanji, wake up! I want food!"

"I thought the goal was to become the greatest swordsman alive," Nami muttered. She pried Sanji's fingers off the candle that he was somehow still gripping.

"Nami-san," Sanji murmured. "I held it for you. A lovely face like yours should never be in the darkness."

"We don't need candles anymore," Luffy announced, "we just need meat! Let's go!" He bounded without a care into the dark, swirling portal, still carrying Sanji in his arms. The rest of his crew, two short, followed him, because that's what they always did.