It is prophesied that a human champion will possess the Heavenly Sword. Long ago, the Raven Lord waged war relentlessly to seize power. However, at humanity's darkest hour, a valiant warrior descended from the skies. This champion clashed with and ultimately vanquished the Raven Lord using the Heavenly Sword. Once the battle concluded, the warrior vanished, leaving the sword behind. Since then, many men have battled fiercely, eager to claim the sword's extraordinary might. Eventually, the responsibility of safeguarding the Heavenly Sword lay with an ancient clan of nomadic warriors, ensuring it would not fall into the wrong hands.
The narrative of the film loosely parallels that of the associated video game. The story opens with Nariko, a member of the same clan tasked with guarding the Heavenly Sword. Regrettably, she is labeled a disappointment, particularly by her father, Shen, who dismisses her combat prowess solely due to her gender. Her skill in battle is undeniable, but it goes unrecognized by Shen, who believes that a daughter is not worthy of honor.
When King Bohan’s assassins breach the clan's fortress, Nariko rises to the occasion, showcasing her fighting abilities by dispatching numerous assassins and rescuing Kyo. King Bohan seeks the Heavenly Sword, for it is the only weapon potent enough to eliminate him. Acknowledging Nariko's skills for the first time, Shen entrusts her with the Heavenly Sword, directing her to journey west while he and the remaining clan members head east.
However, their escape is thwarted when the bridge collapses, leaving Bohan waiting on the other side. He demands the sword's surrender or threatens to kill Nariko, her father, and her sister, Kai. In a shocking twist, Nariko discovers that Kai is her sister, born out of Shen’s quest to rectify the disappointment of having Nariko as his firstborn. Shen had sought to father a son, impregnating various women, as a misguided attempt to create a legacy.
Amidst this backdrop, an unexpected revelation emerges. Two days before Christmas, among the women Shen deserted, one bore a son—unbeknownst to Shen—who would ultimately prove to be the chosen one. For two decades, King Bohan has relentlessly pursued this figure.
As the moment of confrontation with Bohan approaches, Nariko hesitates but then resolves against surrendering the sword, opting instead to leap down a ravine. Her birth, marked by the passing year of the Firehorse, had initially brought disappointment to Shen, who exiled her to the forest. There, Prophet Takashi secretly groomed her into a formidable fighter.
Upon awakening near a campfire, Nariko finds her sister Kai, who had the foresight to rescue her. Though Kai has long known of their blood relation, she kept it hidden because Shen had refused to embrace her role as a father. United, the sisters set out on a journey north to seek out their brother.
Along their trek, Nariko learns of their mother’s resilience and humor—a stark contrast to the coldness Shen exhibited. He would often visit and bring gold, claiming it was for their support. The arrival of Flying Fox marked a tragic turn, as he murdered their kin and left their mother in hiding.
Their quest leads them to a desolate fishing village, where they confront General Whiptail and her soldiers, who have ravaged many innocent lives. With Nariko wielding the Heavenly Sword and Kai equipped with a crossbow, they manage to aid the villagers in their resistance, obtaining crucial directions to their brother. However, they soon find that Loki, their sibling, has left for the northeast in pursuit of work as a blacksmith under a foreign king.
Eavesdropping on their conversation, Whiptail orders her troops to eliminate the sisters. After an intense battle, they succeed in defeating Whiptail, but her warning echoes in their minds: whoever informs Bohan of Loki's location will receive untold rewards.
As they reach the northeastern fortress, Bohan’s forces are already alert. The toll of wielding the Heavenly Sword begins to take a devastating toll on Nariko, as it gradually drains her essence. They uncover a shocking truth: Loki’s newfound king is none other than Bohan. Shen, the girls learn, has been captured and the lies surrounding their lineage unravel.
In the stronghold, they manage to rescue Takashi and other clan members, only to hear the tragic fate of Kyo, who fell to Bohan’s army while attempting to protect them. Shen reflects on the erroneous choices of his past, and with the sisters' forgiveness, he accepts his failures. As he succumbs to his injuries, Nariko harnesses the sword’s potent magic to revive him, despite the worsening consequences this power exacts.
Nariko and Kai arrive at Bohan's blacksmith forge too late. The couple they once assisted betrayed them for riches. However, in a deft rescue, Nariko saves Loki, while faced with the reality of loss as Bohan's son is slain in the commotion. The subsequent battle leads to tragedy, as Loki is struck down, followed by Kai’s brutal encounter with Flying Fox. Yet, in a climactic turn, Kai manages to strike down Flying Fox herself.
The sisters embark on a treacherous journey back to their homeland, pursued relentlessly by Bohan's minions. Upon their arrival, Nariko, weakened, informs Shen of the grievous news—their son is lost, and Bohan’s forces draw near. In a moment of reflection and resolution, she declares that she will not fight for the clan but for Kai, her sole true family.
In what becomes a pivotal moment, Bohan’s army finds them as Nariko learns that Kyo, presumed dead, has betrayed not only her but the clan as well. He cooperated with Bohan, believing that his surrender would lead to the clan's salvation. As arrows rain down from Bohan’s soldiers, Nariko employs the sword's power for protection, but Kyo suffers a fatal blow.
Left to face Bohan’s army alone, Nariko unleashes the full might of the Heavenly Sword, mirroring the formidable power displayed at the film's outset. In an otherworldly moment, she is drawn into the sword itself, confronted with a bitter enmity. Yet, she boldly asserts that Bohan aims to destroy the sword, reaffirming that its power is intricately tied to her survival against his forces.
In a final confrontation, Bohan seizes his own fate, sacrificing his soul to the Raven King. Ultimately, Nariko prevails against him, witnessed by Roach, who threatens her life but is dismissed. Upon returning home, Nariko tells Shen that the sword did not choose her; she chose it willingly. In a final act of tenderness, she uses the sword’s healing abilities to restore a dying Kai.
With her last breath, Nariko implores Shen to show Kai the love he failed to give to her. In her poignant narration, she expresses hope, knowing Kai will embrace the legacy of the Heavenly Sword. Though the sword may fade from memory, Kai's spirit will endure, symbolizing their shared journey and the bond of sisterhood.
As the credits roll, Kai emerges, brandishing the sword with a confident smile, promising to uphold Nariko's legacy, carrying forth the mantle of the Heavenly Sword for a new generation.
