Shinobi: Heart Under Blade

Two rival ninja clans, Iga and Koga, live deep in the mountains honing their skill to superhuman levels. The clans do not live peacefully, and are prohibited by imperial decree from sharing any techniques. Viewing the powerful clans as rivals, a plot is formed to stoke the rivalry to greater intensity. A contest is created between the two clans, but it is not a friendly competition, it is a duel to the death.