Set in feudal Japan, the story is based on the Siege of Oshi and depicts the struggle of Oshi's villagers in defending their fortress against Toyotomi Hideyoshi's campaign against the Hojo clan. Against insurmountable odds, Narita Nagachika, the fortress's castellan, leads a group of 500 men against 20,000 men led by Ishida Mitsunari, part of Toyotomi clan's greater army of 20,000 samurai.