to be fair, I am not sure it is "historical accurate" - as far as my understanding goes, the historical figure didn't "travel" to Japan - he was deported/sold there.
Different sources make different claim about the whole "he was made samurai/ he was a regular soldier / he never fought anything big", but imho then you have to define "samurai" in the first place (during Japan history it went from "mostly a soldier at the service of someone" to some form of "noble status" - see the whole Seinan Sensō).