The rigidity of the samurai as a class varied largely depending on when you're looking in Japanese history. In the Heian Court period, samurai were just armed p

The rigidity of the samurai as a class varied largely depending on when you're looking in Japanese history. In the Heian Court period, samurai were just armed people in the service of Japanese nobility (deriving authority through relation with the Emperor who was considered to be descended from God.) After the Genpei War the samurai became more hereditary until the Sengoku/Warring States Period. Several of the key players during this time were themselves just peasants. Then after Tokugawa took over, he once again encouraged the hereditary samurai as a way to ensure stability. Yasuke was under Nobunaga who was very much active when the definition of samurai was much more fluid than rigid.