A nuance to Cruise's character is that he was already a superior soldier and warrior, a living legend in his own culture. Yet he had become disillusioned. It was insinuated that he had eventually seen the lie of white supremacy behind manifest destiny in the Americas. And no longer saw the native people he had spent his life fighting as "savages".
His character arc seems more about a warrior trying to find an honorable way to live after having spent his life in a dishonorable war. He takes to the samurai way of life so well because he was practically a brother by a different mother.
There are definitely themes of not allowing the past to be distorted and covered up. There's a big shot across the bow at American history in the opening; how the conquest of the Americas had been framed with racist revisionism, erasing crimes against native peoples.
Yeah, exactly. The whole movie directly attacks American colonialism. It's not a white savior thing at all. If anything, it's the white guy being saved from himself and the "American way" by leaving his life to live with the samurai.
Tom Cruise's character, one of their top soldiers, is actually a suicidal alcoholic due to guilt for the things he has done, as well as loathing for the people who commanded him to do those things. He pointedly tells one of his commanders that he would kill him for free if he could. He only finds peace by entirely leaving the American way of life and his American identity.
The people the other Americans see as savages are painted as a cultured, noble people, and the Americans are then shown as the savages (who think they are the cultured ones) who are coming in to run it all over for the sake of their own interests. The whole plot progression of the movie is turning around the whole "cultured people vs savages" narrative that the Americans were touting, and showing that it was the Americans who were the savages. That's why Tom Cruise ends up siding with the Japanese and fighting the Americans in the end.
The ending of the movie shows that the emperor finally learned to resist the Americans' bullshit because of the advice of his samurai. It's a bittersweet ending because the samurai had to die to do it, but in the end the emperor's decision to turn away the Americans saved the samurai's values.
