Jeanne Kaguya d'Arc senses the coming of the Saviour-King through a divine prophecy. Led by Leonardo da Vinci, she embarks for the Star of the East. There, a young warrior named Oda Nobunaga stood in the midst of a battlefield. Powerless against the forces of a neighbouring land ruled by the Takeda, Nobunaga experiences the senselessness of war and senses the dawning of a new era.

Nobunaga has a premonition that the Giant War Armour unit, The Fool, is a force heralding a new era. His confidant, Akechi Mitsuhide, is less certain, but Nobunaga only laughs off Mitsuhide's concerns.

Jeanne Kaguya d'Arc is now with the Oda clan. To attract less attention to herself as a foreigner, she disguises herself as a man named Ranmaru. Ranmaru cannot help but doubt Nobunaga due to his reckless behaviour, but Nobunaga's brother, Nobukatsu, asks Ranmaru to support Nobunaga. Meanwhile, Takeda Shingen goes forth into battle in his Giant War Armour, Fuurin Kazan, in order to test Nobunaga's mettle.

Himiko of Yamatai has averted a crisis by giving Nobunaga a Regalia. However, in return, she demands that they wed. Nobunaga decides that an alliance with Yamatai will strengthen the Oda, and accepts. Meanwhile, as da Vinci plans their betrothal ceremony, Ranmaru seeks to confirm her prophecy by determining whether Nobunaga is the Saviour-King.

As the inevitable clash between the Takeda and the Oda forces nears, Nobunaga and Nobuhide have a clash of their own with differences in opinion regarding tactics. Nobunaga is certain that The Fool should be taken on the offensive, and begins to rally the men. However, someone poisons him with a paralytic, and he collapses. As Nobunaga realises the truth behind the subterfuge, Nobuhide goes forth in his own Battle Armour to duel the Fuurin Kazan...

While the Oda clan struggles with grief over an irreparable loss, Nobunaga disappears. His absence heightens the tension between Mitsuhide and the advisors.