Island villagers find a young woman and young man swept ashore near their remote village in northeastern Japan. The two have tried to escape the girl's enforced marriage to another man, in order that they may marry themselves. The ancient custom of the village decrees that the angry sea gods must be calmed by throwing the pair back into the sea. The lovers face being sacrificed to the sea gods or perhaps something even more difficult to bear.

In the 16th Year of Keityo (1611), the lord of Ogura Castle in Kyushu admitted Sasaki Kojiro's because of his great sword techniques. However, a group within the feudal clan which supported to use guns considered Kojiro an obstacle in their goals and has the well-known ronin, Miyamoto Musashi, fight him. Now because of political gain and greed, two honorable men are to fight to the death on Ganryu Island.