Kagemaru, a central figure from Sanpei Shirato's manga and its 1967 film adaptation, operates as a ninja of the Shadow Clan (Kage ichizoku) during Japan's tumultuous Sengoku period around 1560. He possesses exceptional martial skill and strategic cunning, frequently utilizing deception like kagemusha body doubles. Trained under Mufū-Dōjin within an illegitimate lineage of the shinkage-ryū tradition, Kagemaru stands opposed to feudal warlords such as Oda Nobunaga. His driving motivation is solidarity with oppressed peasants and farmers, leading him to orchestrate rebellions (ikki) aimed at dismantling the exploitative feudal hierarchy.

Kagemaru forms a complex alliance with Jūtarō Yūki, who seeks vengeance against the Iga ninja Shuzen Sakagami for slaughtering his family. After Kagemaru rescues Jūtarō from Shuzen's sister Hotarubi—a clash costing each combatant an arm—he aids Jūtarō's assault on Fushikage Castle. Kagemaru subsequently destroys the castle, exposing the conflict between Jūtarō's goal of status restoration and his own objective of systemic overthrow.

Kagemaru's sister, Akemi, becomes Jūtarō's love interest. Her death during a Kage ichizoku mission leads Jūtarō to initially blame Kagemaru, intensifying their strained relationship. Kagemaru later reveals his familial bond to Akemi to counter these accusations. An enigmatic and morally ambiguous figure, Kagemaru manipulates events from the shadows, leveraging peasant uprisings to destabilize warlords like Nobunaga. His methods involve intricate layers of deceit, and while he fights alongside the oppressed, his alignment remains pragmatic rather than purely ideological. The narrative concludes without resolving his personal journey, emphasizing his role as a catalyst for broader societal conflict.