He's one of the very few confirmed surviving "loyalist" combat veterans of the Betrayal at Honnoji, where Oda "The Demon King" Nobunaga, Japan's first of the "Three Unifiers," was ambushed by his own general.
And while Japan was very much as racist and classist as everyone else, Oda Nobunaga genuinely seemed to be open to a meritocracy and some cultural pluralism if it got him closer to becoming Shogun - while he and the other daimyos were already mass producing their own guns, he still maintained positive relationships with European missionaries and merchants, and his greatest general and de facto successor (the second of the Three Unifiers, Toyotomi Hideyoshi) had started off as a peasant.
Now, Oda was still a vicious bastard in his own right, and also more capricious and bullying as well in a way appropriate to the ignorance and violence of the times- he demanded Yasuke be washed repeatedly to see if his skin color would lighten up, and called his peasant-born general "Bald Rat"...
...But both men served him faithfully in life, and Yasuke even did so after Nobunaga's death; he was protecting one of Nobunaga's sons against multiple attackers after his lord's suicide, and had to be negotiated into surrendering rather than be killed or forced to run away.