[Jiggly]

I would say the differentiation is more based on their "job" and status as Oni said. Not everyone carrying a katana/sword is a Samurai or Ninja. There were also the Sohei, Ashigaru and Ronin among others.

You could say the main character in this show is a Ronin, since he failed to protect his master from being killed. He became a wandering mercenary (Ronin).

Bakumatsu Kikansetsu Irohanihoheto