I don't know much about ninjas outside of what GI Joe taught me. I didn't even think they were real things. I've always been more fascinated with Samurai myself.
My favorite thing about them is that they routinely meditated on their own deaths because this made them more fearless in combat. I love that.
Also, they were pedophiles who had loving sexual relations with their proteges. Not my favorite thing about Samurai, but interesting.
Gay Pedo Samurai
Also too, I love the Kurosawa films about them and Afro Samurai