In the final years of Japan's Bakumatsu period, as the conflict between the Shogunate and those seeking to restore imperial rule reaches its bloody peak, a young swordsman named Himura Kenshin has become a feared legend. Known as Hitokiri Battosai, he is an assassin for the Choshu clan, executing key figures of the Shogunate with a cold, ruthless efficiency that has left him emotionally hollow. The film, set primarily in Kyoto in 1864, follows Kenshin during this dark chapter of his life, before he becomes the wanderer who vows never to kill again.

One night, after a brutal assassination, Kenshin encounters a quiet, enigmatic woman named Yukishiro Tomoe. She witnesses the aftermath of his violence with a strange, unnerving calm. Soon after, Tomoe is inexplicably introduced into Kenshin’s life when Choshu leader Katsura Kogoro assigns her to live with him as a decoy wife, sending them both to a remote village in Otsu to hide from the elite Shinsengumi police force. What begins as a tactical arrangement slowly deepens into a genuine, tender relationship. Kenshin, who has known only death, begins to feel a sense of peace and humanity, while the reserved Tomoe starts to lower her emotional guard. For a brief time, they find solace in a simple life together, believing they have escaped the bloodshed.

However, this fragile happiness is built on a devastating secret. Tomoe is a spy sent by a shadowy group known as the Yaminobu, who are opposed to the Choshu clan. Her mission is to monitor and ultimately orchestrate the death of the man who killed her first fiancé, a samurai lord that Kenshin slew in an earlier mission. As she lived alongside Kenshin, her thirst for vengeance was slowly replaced by genuine love, placing her in an impossible position. The Yaminobu, led by Tatsumi, decide to use her as bait to trap and kill the Battosai.

The narrative builds toward a tragic climax in a snowy, isolated field. Kenshin, realizing he has been betrayed and that Tomoe has been taken, fights his way through the Yaminobu assassins. In the final, chaotic moments of the battle, Tomoe throws herself between Kenshin and a fatal attack from the enemy leader. As she dies in his arms, she reaches up and, with her small knife, cuts a second line across the scar on his cheek, completing the cross-shaped wound that will forever mark his face. Her final act is not one of betrayal, but of protection and love. Overwhelmed by grief and guilt for having killed the one person who brought him light, Kenshin is forever changed. This event solidifies his resolve to abandon his life as an assassin and begin his long journey of atonement as a wandering swordsman who protects the innocent without taking lives, setting the stage for the events of the earlier films.