There was an island in the Grand Line, deep in the Grand Line, so deep that few ever got there from where they started at Reverse Mountain – and it wasn't on any of the standard routes given by the log poses either, so it was even harder to find. On this island, the World Government had little presence, and people who called themselves 'ninja' were everywhere. The island was a large one, divided up by those who lived on it into several countries and each of these countries ruled by a different lord who answered to the emperor of the island, who dealt with the World Government as required, but only when it was required.
When Shanks lost his arm to the Sea King, saving little Luffy, Shanks had his navigator charter a course to that island. It was actually easy to do from East Blue, provided the ship had a logue stone hull and a crew willing to be put to oar. These weren't things that Shanks had though, so they'd be going the long way around to get there. Not that anybody really bothered the Red Hair Pirates if they knew what was good for them.
It took them three years to reach the island that called itself 'The Elemental Nations', and while Shanks sent his crew around to a small harbour on the coast of an area called the 'Land of Rivers', he himself ventured into the deserts of the 'Land of Wind'. His target was the ninja village of Sunagakure.
"What is your business here?" demanded one of the guards at the gate.
"I want a new arm," Shanks answered, shifting his black cape slightly so that the two guards could see that he was lacking said left-side appendage.
The guards nodded and waved him through with directions to where he could find the market district for the parts and the Puppeteers Academy where he could learn to manipulate it properly with chakra strings, so that it would work just like a normal arm – with practice of course.
Shanks was only in Sunagakure for two days before there was an uproar over a puppeteer called Sasori killing the Sandaime Kazekage. Despite this being practically a public service, the man was still forced to effectively go on the run.
Shanks collected all the puppet parts that made up his new prosthetic arm, and followed after the other red-head as fast as he could. If he could convince this Sasori to join him on his ship, even just for a while, then Shanks and his crew wouldn't have to be stuck, attached to this island like they were. Shanks would be able to have someone on board teaching him now to use his new arm.
When Shanks caught up with Sasori, it was to find the man essentially embalming the man he'd killed. Of course, he wasn't about to let that put him off.
"If you have come to kill me -" Sasori began, his tone promising a slow and agonising death, though he didn't halt his work or turn around.
"I haven't," Shanks cut in. "I came to offer you a place on my ship."
"Yep," Shanks agreed. "I still need some training in how to use my new puppet arm, but I don't particularly feel like being stuck on land for that long. I figure if you joined my crew, that would be a win for both of us."
"Your crew. Your ship. You are the captain of this ship then?" Sasori asked.
"Yep," Shanks said again. "Red Haired Shanks, captain of the Red Hair Pirates."
Sasori snorted. "So everybody on your ship has red hair?" Still he did not turn around.
"Nah!" Shanks answered, grinning. "Just me. Well, you as well if you join us."
Sasori hummed quietly a moment, still not turning from his task. "I am turning the Sandaime Kazekage into a puppet," he announced. "This way, I will have his abilities at my disposal."
"Interesting," Shanks answered, shrugging his shoulders behind the other red-head's back. Really, what did that have to do with him?
"Will my turning people into puppets be a problem?" Sasori asked, only just turning his head enough to watch Shank's reaction.
Shanks shrugged again. "Eh, it will probably net you a large bounty if the marines find out about it. Just enemies though, right?" he queried. "I'm rather partial to my crew just as they are."
Sasori nodded. "Only those killed in battle who were worthy opponents," he said, turning back to his task. "I will not waste my time preparing canon fodder puppets."
"Uh-huh," Shanks said, nodding slowly. "So you'll join us?"
Sasori shrugged and finished his task, then sealed away his human puppet. "I will," he agreed.
The Grand Line would never be the same.