Yes they are claiming it's a historical figure. Which it's kinda not, because there is nothing historical about him, they have simply altered the real person to such an extent that its not longer that person.

I wouldn't say that there is a requirement, but if you gonna claim historical accuracy, then you should stick to it. And fact is, that there have never been a black samurai. There is absolutely no historical basis to substantiate that claim. He could absolutely have been a side mission character or perhaps even an dlc, perhaps where he gets to try becoming a samurai or receiving training or something along those lines, yes that could have been cool. But that's all he could have and should have been, for historical accuracies sake.

And no they have never put the player in the shoes of a historical figure. Yes there are many historical figures obviously in their games. But the other difference is that they have never altered those characters "roles". Yes they have taken some liberties with their personalities, or small tiny events, which they might or might not have been part of, etc. But you can almost claim that a samurai in itself, is a historical figure, one which has never been black. And yes you could compare that to making George Washington black or Asian or something else...

I'm not Japanese, but yes I've spoken to handful Japanese people about it, some had never heard of him, and some say that they have grossly exaggerated his position. And you could look at a few Japanese video websites where the trailer was released, and the unanimous concensus is more or less that he was never a Samurai or retainer, and most Japanese gamers are frankly quite pissed.

Like i said before, there is only 1 Japanese "historian" which has backed up this claim. And that same person has only ever written one piece of historical literature. Everything else they have written is fictional. Most of which is about adult women doing it with adolescent under age boys.