"General Onimaru" is a historical manga series set in Japan's Sengoku period, a time of intense social upheaval and military conflict. The narrative centers on Onimaru, a formidable warrior and tactician whose reputation as a fearsome general earns him both admiration and fear. Onimaru's rise to power is marked by his unyielding determination and strategic brilliance, as he navigates the treacherous political landscape of warring states. His ultimate goal is to unify the fractured nation under a single banner, a vision driven by a desire to end the chaos and suffering plaguing the land.

The story explores Onimaru's complex relationships with allies and adversaries alike. Key figures include his loyal retainers, who share his vision of a unified Japan, and rival warlords who challenge his authority. Among these rivals is Takeda Shingen, a cunning and ambitious daimyo whose clashes with Onimaru form a central conflict in the series. The narrative also delves into Onimaru's personal struggles, including his internal conflict between his ruthless ambition and his lingering sense of humanity.

The plot is driven by large-scale battles, intricate political maneuvers, and the shifting alliances characteristic of the Sengoku period. Onimaru's campaigns are depicted with a focus on both the strategic and human elements of warfare, highlighting the sacrifices and moral dilemmas faced by those involved. The series also incorporates elements of Japanese folklore and mythology, adding depth to its portrayal of the era.

As the story progresses, Onimaru's journey becomes increasingly intertwined with the fate of Japan itself. His victories and defeats shape the course of history, culminating in a climactic struggle that will determine the future of the nation. The series balances its grand historical scope with intimate character moments, offering a multifaceted portrayal of its protagonist and the world he seeks to transform.