European mercenaries searching for black powder become embroiled in the defense of the Great Wall of China against a horde of monstrous creatures.

Kai—an outcast—joins Oishi, the leader of 47 outcast samurai. Together they seek vengeance upon the treacherous overlord who killed their master and banished their kind. To restore honour to their homeland, the warriors embark upon a quest that challenges them with a series of trials that would destroy ordinary warriors.