"Blade of the Immortal" is a dark and intricate manga series set in feudal Japan, blending historical elements with supernatural themes. The narrative centers on Manji, a skilled samurai cursed with immortality after a series of brutal battles. His immortality is granted through "bloodworms," mystical creatures that heal his wounds and prevent death. Haunted by the guilt of killing 100 innocent people in his past, Manji seeks redemption by vowing to kill 1,000 evil men to atone for his sins.

The story gains momentum when Rin Asano, a young woman, seeks Manji's help to avenge her parents, who were murdered by the Ittō-ryū, a rogue sword school led by the enigmatic Anotsu Kagehisa. Anotsu aims to dismantle the traditional samurai hierarchy by uniting outcasts and creating a new order, challenging the established feudal system. Rin's determination and Manji's quest for redemption intertwine as they pursue Anotsu and his followers, navigating a morally ambiguous world where the lines between good and evil blur.

Throughout the series, Manji and Rin encounter a diverse cast of characters, each with their own motivations and backstories. These include Hyakurin, a former prostitute turned warrior; Taito Magatsu, a disgraced samurai with a tragic past; and Makie, a deadly swordswoman with a complex relationship to Anotsu. The narrative explores themes of vengeance, justice, and the cost of immortality, often delving into the psychological and emotional toll of violence.

The plot is structured around episodic confrontations with members of the Ittō-ryū and other adversaries, interspersed with flashbacks that reveal the characters' histories and motivations. The series is notable for its graphic depictions of combat, intricate swordplay, and morally ambiguous characters. As Manji and Rin progress on their journey, they face increasingly formidable opponents, culminating in a climactic confrontation with Anotsu and the unraveling of his grand vision.

"Blade of the Immortal" is a sprawling tale that combines historical drama with supernatural elements, offering a gritty and thought-provoking exploration of humanity, morality, and the consequences of violence. The series is marked by its complex characters, intricate plotlines, and unflinching portrayal of the brutal realities of its world.