The story tells of a group of samurai after their daimyō (feudal lord) Asano Naganori was compelled to perform seppuku (ritual suicide) for assaulting a powerful court official named Kira Yoshinaka after the court official insulted him.

After waiting and planning for a year, the rōnin avenged their master's honor by killing Kira. Anticipating the authorities' intolerance of the vendetta's completion, they were prepared to face execution as a consequence. However, due to considerable public support in their favor, the authorities compromised by ordering the rōnin to commit seppuku as an honorable death for the crime of murder.

This true story was popular in Japanese culture as emblematic of the loyalty, sacrifice, persistence, and honor (qualities samurai follow called bushidō) that people should display in their daily lives. The popularity of the tale grew during the Meiji era, during which Japan underwent rapid modernisation, and the legend became entrenched within discourses of national heritage and identity.

Fictionalized accounts of the tale of the forty-seven rōnin are known as Chūshingura. The story was popularised in numerous plays, including in the genres of bunraku and kabuki. Because of the censorship laws of the shogunate in the Genroku era, which forbade portrayal of current events, the names were changed. While the version given by the playwrights may have come to be accepted as historical fact, the first Chūshingura was written some 50 years after the event, and numerous historical records about the actual events that predate the Chūshingura survive.

The bakufu's censorship laws had relaxed somewhat 75 years after the events in question during the late 18th century when Japanologist Isaac Titsingh first recorded the story of the forty-seven rōnin as one of the significant events of the Genroku era. To this day, the story remains popular in Japan, and each year on 14 December, Sengakuji Temple, where Asano Naganori and the rōnin are buried, holds a festival commemorating the event.

In late-medieval Japan, Kai is a half-Japanese and half-English outcast who gets saved by Lord Asano, the benevolent ruler of the Akō Domain. Kai and Asano's daughter Mika fall in love, despite the scorn her father's samurai hold for Kai’s mixed ancestry.

Lord Kira, the Shōgun's master of ceremonies, seeks to take Akō for himself with the help of Mizuki, a shapeshifting kitsune. She sends a kirin to kill Asano and his men on a hunting trip, leading Kai to ride to their aid. Taking up a fallen sword, Kai slays the monster and spots Mizuki in the form of a white fox with different-colored eyes.

When the Shōgun Tokugawa Tsunayoshi visits Akō, Kai notices Mizuki disguised as a concubine with the same multi-colored eyes. He tries to warn Asano's principal counselor, Oishi, about the witch in Kira's household, but is dismissed.

For the entertainment of the Shōgun, Kira arranges a duel between his best warrior, a golem, and Asano's chosen combatant, whom Mizuki incapacitates with magic. Kai secretly dons his armor to fight in his stead, but is unmasked during the duel, and the Shōgun orders him severely beaten. That night, Mizuki bewitches Asano into believing Kira is raping Mika, causing him to attack the unarmed lord.

Sentenced to death, Asano is compelled to perform seppuku to preserve his honor. The Shōgun gives Kira domain over Akō and Mika, granting her one year of mourning before she must marry Kira. The Shōgun brands Oishi and his men ronin, forbidding them from avenging Asano, and Kira has Oishi imprisoned and Kai sold into slavery.

Nearly a year later, Oishi is released by his captors, believing him harmless. Having realized that Kira used sorcery to frame Asano, Oishi and his son Chikara reunite the scattered ronin, and rescue Kai from the fighting pits of the Dutch colony of Dejima. Kai leads them to the mystical Tengu Forest, which he escaped as a child, to obtain the special blades of the Tengu.

Warning Oishi never to draw his sword inside the Tengu temple, Kai faces the Tengu Master who once trained him. Faced with an illusion of his men being slaughtered by the Tengu, Oishi resists the urge to draw his sword, while Kai bests his former master. Having proven themselves worthy, the ronin receive their blades.

They plan to ambush Kira on his pilgrimage to a shrine to seek blessings for his wedding to Mika, but the procession is a trap and most of the ronin are killed. Believing them all dead, Mizuki presents Kira with Oishi's sword, and taunts Mika with their deaths. Oishi and Kai, having survived the attack, lead half the remaining ronin to infiltrate Kira's castle, disguised as a band of wedding performers.

With Kira's men distracted during the performance, the other ronin scale the castle walls and attack the guards. While Oishi fights Kira, Kai and Mika face Mizuki in the form of a dragon, and Kai finally draws on the mystical powers of the Tengu to kill her. Oishi emerges with Kira's severed head, and Kira's retainers surrender.

The ronin and Kai surrender themselves to the authorities of the bakufu and are sentenced to death, having violated the Shōgun's prohibition on avenging Asano. However, the Shōgun declares that they followed the principles of bushido and restores their honor as samurai, allowing them to perform seppuku and receive the honor of burial with Asano. The Shōgun returns domain of Akō to Mika, and pardons Chikara so that he may preserve Oishi’s bloodline and serve Akō.

An epilogue explains the tradition of paying respect at the graves of the 47 Ronin, which continues every year on December 14.