2014, fifteen years after a war between Earth and Mars. Desiring peace, Princess Asseylum of Mars holds a goodwill parade on Earth. Slaine a boy originally from Earth prays for her safety Meanwhile, on Earth, high school student Inaho and his friends receive pilot training in combat robots called Kataphraktos.

The Landing Castles of the Mars Knights that have landed on Earth launched an attack using Kataphraktos with the aim of invading the planet. The United Forces of Earth launch a counteroffensive. As the fierce battle rages on, Inaho encounters a mysterious girl.

To complete his plan, the Mars Knight relentlessly pursues Inaho and the others. Inaho is suspicious about the manner in which that knight fights. With backing from Marito’s group, Inaho begins a counteroffensive. Meanwhile, Slaine, unaware of the truth, has been ordered to provide support for the Mars Knight and is out in the field with him.