In 1600, at the Battle of Sekigahara, Tokugawa Ieyasu is assassinated by a ninja under the command of Shimazu's general Shima Sakon. The Tokugawa camp realizes that if Ieyasu's death becomes known, morale will shatter and the chance to unify Japan under Tokugawa rule will be lost. As a desperate measure, they install a body double: Jirosaburo, a wandering warrior who has served as Ieyasu's shadow for ten years. Jirosaburo is no ordinary stand-in—he was once a fierce warrior in the Ikkō-ikki rebellion who famously shot Oda Nobunaga, and over a decade of mimicking Ieyasu he has absorbed the shogun's battle tactics, political cunning, and even his mannerisms.

The story follows Jirosaburo as he fully assumes the identity of Tokugawa Ieyasu. He must lead the Tokugawa forces through the aftermath of Sekigahara, outmaneuver rivals like Ishida Mitsunari, and maintain the deception against spies, allies, and even Ieyasu's own family. Key retainers such as Honda Masanobu and the aged but brilliant strategist Shima Sakon (now an ally) support him, but cracks appear as the double's past resurfaces and the true heir, Tokugawa Hidetada, grows suspicious. The narrative arcs include the cover-up at Sekigahara, the consolidation of power in Edo, and the delicate balance between impersonation and genuine leadership. As Jirosaburo becomes more entrenched in Ieyasu's role, he faces a question that defies history: can a shadow become the ruler in truth, and what happens when the lie threatens to outlive the man it was meant to save?