About forty years ago, humans discovered the technology of the prehistoric civilization "Aldnoah" on Mars. With the progress of Mars colonization and the claim of technological monopoly, the friction between the Martian pioneers and the Earth has expanded. In 2014, Earth and Mars, which were in a truce, were negotiating for peace. Princess Esser Iram (voiced by Amamiya Sora) of the Martian "Weiser Empire" visited Earth as a goodwill ambassador to make efforts to break the ice. However, her parade car was attacked by missiles from terrorists in Shin-Awara City, Japan. The Martian Empire regarded it as a declaration of war from Earth and immediately launched attacks on various countries on Earth, and the war between the two planets broke out again. Inaho Kaizuka (voiced by Natsuki Hanae), a high school student on Earth who has been trained in fighting skills and humanoid combat weapons, joins the battle of the mecha cavalry with his companions. At the same time, the princess's attendant Slaine (voiced by Kensho Ono) is also involved in the war and works hard to rescue the princess of the empire.