In the early 18th-century, Lord Takuminokami Asano, feuding with Lord Kira, tries to kill his opponent in the corridors of the Shogun's palace. The Shogun sentences Asano to seppuku and deprives the palace and lands from his clan, but does not punish Kira. Asano's vassals leave the land and his samurais become ronin and want to seek revenge against the Lord's dishonour. But their leader Kuranosuke Oishi seeks to restore the Asano clan with his brother Daigaku Asano. One year later, the Shogun refuses, and Oishi and 46 rōnin are out for revenge.

An orphan Mihato Mari works as a secretary at a spinning factory.