It was widely understood among the Straw Hat pirates that their swordsman and de-facto first mate Roronoa Zoro had no sense of direction. You could put him on a straight path five meters from the ship, and find him an hour later wandering the mountains wondering how everyone else had gotten lost. Even their captain Luffy, who was not known for his own map reading skills or ability to arrive anywhere on time, had been heard to comment that Zoro had a "mystery sense of direction." The rest of the crew had long tired of shouting at Zoro, and simply found ways to compensate for his disability. These ranged from asking someone to accompany him whenever he left the ship to assigning someone to Zoro-finding duty an hour in advance of when they planned to leave.
Even so, there were times when the depths of Zoro's perpetual directionless-ness became a bit much for any rational person to cope with. And one such time, unfortunately, lost Nami 5000 beri, an event guaranteed to lead to shouting and much pummeling over the head.
As Nami later lamented to Robin over a nice cup of soothing tangerine juice (courtesy of Sanji), "I admit it was partly my fault. I should have known better than to hand Zoro anything valuable. But Sanji was at the other side of town looking at ingredients, and I was in a critical point in my negotiations on the price of that dress. All I asked Zoro to do was go two stalls down and tell the shopkeeper that I had asked for a white paper not cream paper. Two stalls away! It was in plain sight! And yet somehow that idiot manages to find the only fools in town who haven't seen his bounty poster. Oh, and who like to shake people down for money next to a conveniently situated mud puddles. The unfairness of it all! And he didn't even remember to rob them of what money they had, which might have recuperated some of my loses."
Robin was tracing the faint shape of a map along the table with her finger, a pensive expression on her face. "If I'm correct, then to reach that location he was walking in the exact opposite direction of the paper stall."
Nami ranted, "Of course he was! He always goes the opposite direction of where he's supposed to! And then he has the nerve to tell me that he was planning to throw the paper in the air so he could draw his sword and catch if before it hit the ground—with this look on his face like it's my fault that the paper flew in all directions instead of falling straight down—clearly I must have brought defective paper. Aargh!"
Robin said, "What I meant is that it's odd he managed to go in the precise opposite direction that you pointed, instead of taking a wrong turn and ending up more to the side or so. I noticed the same phenomenon on Skypeia. When we were separated, both Luffy and Chopper took some wrong turns in the forest. Chopper got a little sidetracked while Luffy went in loops. But only Zoro managed to go due north when we were trying to go south. He might have gone completely back to the starting point if a giant bird and snake hadn't intervened. Most people who get lost go in circles, while our swordsman always seems to go straight backwards."
Nami said, "So Zoro is a moron. What's new there?"
Robin replied, "If he was merely a moving randomly, then sometimes he should pick the correct path, if only by coincidence. But instead, he unerringly goes in the direction which is most opposite to his destination. Very peculiar. One could almost conclude that he has a very powerful, if defective, internal compass."
Nami opened her mouth, closed it, and thought about this.
Nami got the opportunity to test Robin's theory a week later.
Zoro looked at Nami with some wariness as she approached the place where he was lifting weights on the deck. "What is it now? I already told you that I couldn't chase down those thugs to steal their money because I was too busy trying to catch 365 out of 500 pieces of paper before they hit the ground. I got all the ones that almost fell in the lake, how was I supposed to know that mud didn't come out of paper?"
"Never mind that," Nami said in a distracted voice that would set off all kinds of warning bells to any member of the Straw Hats crew. "You can make up for your mistake by helping me with some shopping again. Hurry up."
The ship was anchored in a small bay next to a forest, with a crude dock. Pirates typically landed there instead of next to the town to avoid marine attention.
Once on solid ground, Nami explained, "There's a road into town up ahead, but the sign fell down, and now we don't know which road goes to town and which one had the warning about the rockslide."
Zoro asked, "So why do I have to be awake for this?"
"Because you're going to help me get to town so I can go shopping. We have a fifty-fifty shot at the right road, so you're going to select one randomly."
Zoro yawned, but under Nami's glare he picked a road and began to walk down it. Nami picked the other path.
Nami had already reached town and brought two new shirts and new sandals by the time the swordsman realized he was alone.
Several days later, the townspeople were delighted to see that someone had cleared out the road buried in rocks for them. Although why the green-haired swordsman had been in such a great hurry to get to the Forsaken Swamps was anyone's guess.
On their next land stop, Nami gave it another test. "Zoro, I need to find out how long it takes the log post to set here. Go ask the harbormaster."
Zoro grumbled but staggered to his feet.
From the crow's nest, Nami watched Zoro leave, making a note of precise direction and distance. Then she turned the map upside down and traced an exact mirror of his path. It finished at the harbormaster's office, at almost the exact same place where Zoro had stopped to get in a fight with a wild bear. Remarkable.
Nami was pacing the deck with worry. Robin had spotted Smoker in town and had sent out Chopper to warn the others to get back to their ship. (Zoro had remained on watch at the ship, thank god, so there had been no need to try to find him in some obscure location.) All had been assembled except for Luffy, whose scent Chopper had lost in a lake. Luckily no one had reported any drownings, so Nami suspected Luffy had gotten on one of the funny swan shaped boats and peddled off to who knew where.
Nami's eyes fell on Zoro, slumped over the deck snoozing, and inspiration struck. She shook him awake. "Which way do we go to find Luffy?"
Zoro's eyebrow twitched in annoyance. "How would I know? I don't have the slightest idea where our captain is any more than you do."
Nami persisted, "But say that you were looking for Luffy. Just pretend. Which direction would you go?"
Zoro turned to his left. "How about this way?"
Nami smiled as she proceeded to drag the swordsman off in the exact opposite direction.
Several more directions from Zoro later, and they found Luffy on a river bank fishing with some old guy (or, perhaps it would be more accurate to say, eating all of the old guy's fish).
Nami prided herself on her ability to detect weather under any conditions, no matter how freaky the air and sea currents of the Grand Line might be. But a man-made storm was a different matter; there had been no meteorological clues at all. She had suspected that something was wrong when the marine ship stopped chasing them, of course, but not enough to stop running away. And then it had been too late.
The Straw Hats had run afoul of a marine captain with the Hurricane-Hurricane fruit, and while Nami had still sensed the air currents change when he activated his devil fruit ability, with only five seconds warning before the sky went crazy there hadn't been much she could do. She had at least managed to keep their ship intact—another pirate ship nearby had been torn to pieces.
Now, everyone on the crew was pitching in to help. Sanji and Chopper struggled with the sail while Brooke and Usopp bailed water. Franky was making some rapid repairs to the side of the Sunny, which had been hit by a broken mast from the less fortunate ship. Luffy and Robin were using their devil fruit powers to deflect more pieces of debris. Zoro seemed to be wandering around uselessly, but he was keeping a close watch in the devil fruit users and had already managed to catch Chopper when he slid towards the rail.
Nami herself was struggling with the steering wheel, looking for any signs of the edge of the storm. If only this were a natural storm, she might be able to keep them safely in the eye of the hurricane, but the winds kept changing direction and moving in patterns that ranged from circular to triangular to insane loopular.
A hard gust sent her backwards, and Zoro's hand caught her back. "Are you steady? Can I let go?" he asked.
"The wheel!" Nami screamed, watching in pinwheel randomly in the wind.
She grabbed on to the wooden wheel. Zoro's hand latched on with her's, helping her hold it steady. "Tell me which way to steer it," he said.
Inspiration dawned. "No, you steer it."
He gave her an odd look. "What? You sure?"
"You're the one who always claims he knows where he's going, don't you? Just do it!"
With a shrug that indicated a profound willingness to put himself at the mercy of fate, Zoro pointed the ship in a random direction.
Nami sent Zoro flying away from the steering wheel with a sharp punch to the head. Then, as he cursed at her, she spun the wheel until they were facing in the exact opposite direction.
The Thousand Sunny-Go made it out of the storm in less than a minute.
"Zoro, which way?"
"Let's go to the left."
"Get over here, we're going right. Okay, another fork in the road. Now where?"
"Why do you keep asking if you're only going to pick the opposite direction?"
"Shut up and answer the question."
"Ug, how would I know. Maybe right this time."
"Left it is, then. It's like having my own human compass…"
"What was that?"
"Nothing. Just keep walking."
And this might have worked indefinitely, if Nami hadn't gotten greedy.
She cornered Zoro after he was heading into a saloon for a drink. "Zoro, I want money. Gold, beli, valuable items, I don't care how."
"And why are you telling me this? You know I don't have any money, so I can't pay off your exorbitant interest rates."
"Doesn't matter. Just go find some money." Nami waved her hands in like she was shoeing him away. "Go on, walk."
Zoro stared at her until he realized that she was serious. Then he took a few tentative steps.
"Don't move!" Nami screamed, pulling out a compass, a protractor, and numerous other measuring tools as she carefully captured the exact direction to the nearest degree that Zoro had moved in. Then she drew a line in the dirt and took off the opposite way, dragging the irritated swordsman behind her.
Nami refused to deviate from this path, no matter the obstacles in her path. She plowed through a group of smoking thugs who narrowly saved themselves by recognizing Zoro from his wanted poster; she used Zoro as a stepping stool to hop over a koi pond, and she climbed straight up and down a house, to the amazement of the elderly couple watching from their porch. And finally…
The two arrived in front of a massive stone building with a sign on front reading, "Redwood Town Bank." A few guards were standing outside the entrance.
"A BANK? I don't believe it!" Nami, who was still dragging Zoro by his collar, dropped him to the ground. "Sure, it has money, but lot of good that does me. Some dowsing rod you are!"
Zoro rubbed the back of his skull. "I've had about enough of this, crazy woman. Next time you tell me to move I'm sleeping through it, and I don't care how many beli you charge me." He began to lumber forward in the direction of the marsh at the edge of the town (one can only assume he thought he was going to the saloon.)
"Wait! You're going the wrong way!"
Zoro merely grunted and kept walking.
Nami pleaded, "Before you leave, you've got to tell me your secret. How do you always go 180 degrees in the wrong direction? Exactly the wrong way, every time?"
"I don't go the wrong direction."
Nami snorted. "You're walking into a swamp! There's a sign right by your elbow that says 'Crocodile Swamp, 25 meters' and an arrow pointing that way. Unless you're illiterate as well as directionless I don't see how you can miss that."
Zoro looked offended. "I'm not illiterate, I don't use signs. I let my instincts guide me."
"If you tried reading a sign for once you might save your nakama a little grief!"
"I always get where I want to be eventually, so what does it matter?"
Nami cast her eyes to the heavens. "God, please explain to me why you gave this idiot such wacked-up instincts? How did you expect him to survive?"
She was waving her hands in a way Zoro found vaguely amusing, but if she kept this up then soon she'd start hitting him again, and Zoro preferred to avoid that. The best way would be to give her what she wanted.
He said, "You know you how you have this instinct in your head, that warns you of danger? If I avoid danger then I'll never get any stronger. So I always go in the direction that my head tells me is bad."
"You mean to say you've been doing this on purpose?"
Zoro nodded. "I told you all along that I had a great sense of direction."
Nami was too busy trying to pinch herself awake to lead them back to the ship, which proved to be a bit of a mistake, seeing how with Zoro walking in front, he managed to lead them both straight into the King Crocodile, a pack of carnivorous birds, and a poison-spitting flower all in the same location. On the bright side, Sanji got to cook his Fleur de Winged Crocodile special that night.
Much later in the evening, Nami complained to Robin over a cup of chocolate mousse, "All this time he was pretending to have no sense of direction, and he was playing me for a fool. And the worst part is, he doesn't even know that he's making a fool of me! He just thinks that his crazy system makes complete sense!"
Robin took another bite of her dessert. "Well, that was always one possible explanation for Zoro's reverse-sense of direction. I had long since concluded that in order for him to be so perfectly wrong he must have a genuine gift for perception of location. He was either misinterpreting his ability or deliberately misusing it. My other theory involved him being under an ancient mystical curse, so it was a little less plausible. Our nakama certainly are an interesting bunch, aren't they?"
"IT'S NOT FAIR! IT'S NOT FAIR THAT SUCH A BLESSING WENT TO AN IDIOT LIKE HIM INSTEAD OF A NAVIGATOR LIKE ME! GOD, PLEASE TAKE AWAY ZORO'S SENSE OF DIRECTION AND GIVE IT TO MEEEEEEEEEEEEEEE!"
Around the ship, six people heard this and thought "What?"
For the next few days, Sanji took extra care over making Nami special delicious and strengthening snacks, Luffy didn't steal them, Franky kept the noise from his work room down, Usopp didn't bother her with any crazy stories, Brooke didn't ask to see her panties, and they all pretended to have a routine check-up with Chopper so that the reindeer doctor would get a chance to examine her. After all, even if she had been acting normal since then, some disturbing evidence pointed to Nami having a mental breakdown.
This attention hadn't exactly escaped Nami's notice, but she considered the truth too horrible to share with the world.
So to this day, only Nami (and Robin) know that Zoro has a great sense of direction.