The rules of this world

When Yasuke was stripped of his title as samurai then exiled for many years he isolated himself within the woods of Japan. One day while Yasuke was gathering wood near a small village and happens to see a boy with the same skin tone as him being beaten for stealing food knowing the hardships that the boy will go through he saves him and decides to take him in and teach him how to be a swordsmen. This is the legend of Mayonaka no musuko