Red Shadow (2001) on Netflix

Plot summary

The Warring States period has set the daimyo Hidenobu Togo and his rivals against one another, and the ninjas of the Kage Clan serve him. The clan forges weapons and armor from a metal called invincible steel and practices mysterious ninjutsu, but the steel is giving out and fewer members can work those techniques. Its remaining legitimate successors are three young ninjas, Akakage, Aokage and Asuka, who train under the leader Shirokage. The lesson handed down through their generations, that a ninja works as a shadow so the world can live in light, sits badly against what Togo orders them to do.