They already wear samurai armour - What do you think the look was based off in Predator 2?
And you're saying all this ... for the thought of a Japanese actor being in the film. You've made the incredible leap from someone Japanese being in the movie, to everything being "Japanese", which is in itself inherently bullshit - You do realise that ninja shit and samurai armour-centric stuff accounts for very, very little of Japanese cinema, right?
Well, obviously not, but seriously - Stop being an ignorant f**k before someone comes along and decides to revoke your posting privileges.