What will it takes to have a Japanese-influenced culture or civilization to exist in the Americas before Columbus' arrival?
This. People always underestimate the Pacific in these threads.A smaller pacific. It is much, much larger than the Atlantic.
Alternately, some early POD that pushes the Jomon or Ainu towards a more maritime orientation, and a slow spread north then east down the west coast of North America.
What will it takes to have a Japanese-influenced culture or civilization to exist in the Americas before Columbus' arrival?
Yes, starving masses migrate faster.
Just like the current Japanese whaling "research" started in the hungry days immediately after WW2.
So starving Japanese are likely to move farther and faster than if they were merely searching for furs and ivory.
Speaking of ivory, Farley a peat wrote a book that speculated about some obscure archeological finds in the Eastern Canadian Arctic. Now at speculated that early European explorers (circa 1,000 AD) were searching for walrus ivory when ivory was worth its weight in gold in Europe. Genuine "unicorn" ... er Narwal tusks commanded an even higher price among European nobility.
Here, along the Southern BC coast, many native faces have traces of Japanese features, which makes me wonder how many Japanese sailors accidentally drifted across the Pacific.
I guess the big question would be why would the Japanese go to the Americas when they have a ridiculously wealthy neighbor far closer to them in China? I mean, the idea of Native American Samurai sounds incredibly awesome, but why go 6,000 miles or so to trade for gold when you could just trade with China or Korea next door? Really, you'd have to either speed up development of Japanese sailing technology or really slow down European sailing technology to make this feasible and you'd probably have to do both. Now, if China were to start charging ridiculous rates for trade and they had an effective monopoly in East Asia, then maybe that might spur a search for alternate sources of trading partners. Honestly, I think the Japanese might find more value setting up lumber and whaling outposts in the Pacific Northwest. Maybe from there, though, you might have some explorers who set up trading posts further and further south and maybe encounter some more advanced civilizations. That might just do it for giving the Japanese motivation to stay in the Americas.
Native American Samurai? I mean the Japanese presence would be at most the equivalent of mountain men and traders who establish frontier Metis families with some Japanese cultural markers remaining that act as prestige skills iron forging being one of them maybe sword making but anything else is rather weeb fanciful dream than probable you know?