I watched a movie with my cousin when I was 7ish. I remember a small and young karate army in an open field wearing simple white kimonos and belts of all colors. They had swords and probably horses. There were some girl fighters too. They were in the field and maybe scared and expecting the enemy. The enemy arrives, wearing black clothes and outnumbering them. The battle is quick and graphic and the karate guys get decimated and one loses his leg and screams in pain. That’s where we stop watching the movie.