Two planets, one to the East and another to the West, were once bound together by a chain called the Dragon Stream. But now, that chain is broken and the two halves are only joined in war. Nobunaga the Fool is heir to the Eastern Country of Owari. Regarded as too foolish and carefree by many, including his friends, Nobunaga is thought to be a nuisance even by his father. A girl from the West named Jeanne Kaguya d'Arc has visions of a "Savior-King." She is accompanied by Leonardo da Vinci as she journeys to the Eastern Planet in search of the person in her visions. Leonardo and Jeanne quickly fall victim to a military confrontation between powerful mecha, only to be saved by Nobunaga. Nobunaga takes control of Leonardo's mecha, intending to warn his family of the siege he suspects. Jeanne suspects that the lackadaisical Nobunaga might be the Savior-King she's envisioned.

High school student Yoshiharu Sagara wakes up and finds himself in the middle of a raging Sengoku period battle. He is saved by the legendary Hideyoshi Toyotomi, but at the cost of the hero's life. With his dying breath, the warrior pleads for Yoshiharu to become a feudal lord in his place. Now that the course of history has been changed, Yoshiharu pledges to keep the timeline from diverging any further. Yet, after rescuing Nobuna Oda—whom he discovers is actually the fabled Nobunaga Oda's female counterpart—Yoshiharu realizes he has been transported to an alternate reality where most of Japan's historical warlords are now cute girls! To set things right and find a way back home, Yoshiharu agrees to become one of Nobuna's retainers and assist her in a conquest of Japan. As Nobuna initiates her campaign, Yoshiharu discovers that the history he learned from playing the video game "Nobunaga's Ambition" allows him to predict future events and turn the tide of war. Using this invaluable gift to aid the Oda clan's beautiful generals, Yoshiharu hopes to help his new lord fulfill her dream and win the hearts of women everywhere. [Written by MAL Rewrite]

High school student Yoshiharu Sagara wakes up and finds himself in the middle of a raging Sengoku period battle. He is saved by the legendary Hideyoshi Toyotomi, but at the cost of the hero's life. With his dying breath, the warrior pleads for Yoshiharu to become a feudal lord in his place. Now that the course of history has been changed, Yoshiharu pledges to keep the timeline from diverging any further. Yet, after rescuing Nobuna Oda—whom he discovers is actually the fabled Nobunaga Oda's female counterpart—Yoshiharu realizes he has been transported to an alternate reality where most of Japan's historical warlords are now cute girls! To set things right and find a way back home, Yoshiharu agrees to become one of Nobuna's retainers and assist her in a conquest of Japan. As Nobuna initiates her campaign, Yoshiharu discovers that the history he learned from playing the video game "Nobunaga's Ambition" allows him to predict future events and turn the tide of war. Using this invaluable gift to aid the Oda clan's beautiful generals, Yoshiharu hopes to help his new lord fulfill her dream and win the hearts of women everywhere. [Written by MAL Rewrite]

In the "one-of-a-kind samurai-general-reincarnated-as-a-canine comedy," Nobunaga perishes at Honnouji as in history, and reincarnates in modern-day Japan as a dog named Shinamon. Other Warring States era warlords such as Takeda Shingen eventually join him, also as dogs. (Source: ANN)