"Iga no Kagemaru" is a historical action manga set in feudal Japan, centering on Kagemaru, a young ninja from the Iga clan. The story begins with Kagemaru's village being destroyed by the rival Koga clan, leaving him as one of the few survivors. Driven by a desire for revenge, Kagemaru trains rigorously to master the ninja arts, honing his skills in stealth, combat, and strategy. His journey is marked by a series of battles and encounters with powerful adversaries, including other ninja clans, samurai, and warlords vying for control over the fractured nation.

As Kagemaru grows stronger, he uncovers deeper conspiracies surrounding the destruction of his village. The conflict between the Iga and Koga clans is revealed to be part of a larger power struggle involving influential figures in the samurai class. Kagemaru's quest for vengeance becomes intertwined with his role in protecting the Iga clan's legacy and ensuring its survival. Along the way, he forms alliances with other skilled warriors, including fellow ninja and rogue samurai, who aid him in his mission.

The narrative explores themes of loyalty, honor, and the moral complexities of revenge. Kagemaru's character evolves from a single-minded avenger to a more nuanced figure, grappling with the consequences of his actions and the weight of his responsibilities. The manga features intricate fight sequences, detailed depictions of ninja techniques, and a richly developed historical backdrop, capturing the political intrigue and chaos of the Sengoku period.

Key characters include Kagemaru's mentor, who imparts wisdom and guidance, and his rivals, who challenge him both physically and ideologically. The story also delves into the relationships between the Iga and Koga clans, highlighting their shared history and the personal vendettas that fuel their conflict. "Iga no Kagemaru" combines intense action with a compelling exploration of its protagonist's growth and the turbulent era in which he lives.