Flying or no, given the relative state of the game world and how it compares to its real-world parallels, that level of movement unassociated with acts of conquest or the like is nearly unheard of until hitting the renaissance, age of sail and colonialism and all that. There was some level of cultural diffusion and knowledge of far-flung places, sure, but it was rarely accurate, and the further apart two areas were the more and more fantastical it all became.

It's like imagining a family of English folk from the 1200s migrating all the way to India, living there and assimilating, and then coming back. Sure, the aristocracy had some knowledge of India, but once you got past the Mediterranean and the Levant it became more a subject of myth and speculation than anything concrete barring an understanding of the spice trade. Nor was England nearly as cosmopolitan to foreigners showing up and just doing their thing as the Romans centuries before might have been.

Then, you add on wings and feathers to the random group of people just showing up and asking to move in in some abnormal language, and if I was an average peasant living in fantasy Japan where the only non-humans I might have much interaction with were still much less distinguishable than harpies are, I might be more inclined to grab a torch and some large farming implement and say "hell no!"

Just to focus even more specifically for this setting - it's even been mentioned before that while diplomats, on official business and all that, [i]do[/i] get to Thaln, Velt, etc. from Akitsushima, it's a long ways and seems fairly rare from what I've gathered. There's a whole continent between this one and Akitsushima that has more contact. Were I you, I'd send some DMs to the GMs and see what you can work out with something more like that. Maybe be our Ibrahim ibn Yaqub rather than our reverse Jan Joosten van Lodensteijn.